Improve handling of sample timestamps automation and non-automation c…

…ases

With platform collectors now being per-global and per-source type, we need a
way to clearly indicate that the "unprocessed" timestamp from a sample (i.e.
what is fed to "relative high resolution time") must be the same across all
globals.

We also need to make sure that this works for both real and virtual pressure
sources.

- The abstract "pressure source" concept added a few commits ago now has an
  accompanying "pressure source sample" concept. It is a struct holding
  implementation-defined telemetry data as well as a timestamp corresponding
  to when it was obtained.
  Functionally, this should be identical to the what the spec has as of pull
  request w3c#280.

- Virtual pressure source's "pending samples" is now a struct as well,
  holding similar data: a PressureState (like before) and a timestamp that
  is set to the "unshared current time" when the "update virtual pressure
  source" endpoint is called.

- The "data collection" algorithm is responsible for reading either a
  "pressure source sample" or a virtual pressure source's "pending sample"
  and processing the timestamp value as necessary.

index.html

@@ -249,6 +249,30 @@ <h3>Sampling and Reporting Rate</h3>
     defined by {{PressureSource}}. A [=pressure source=] can make use of data
     fusion with data from additional sources if that provides better results.
   </p>
+  <p>
+    The telemetry information provided by a [=pressure source=] is represented
+    in this specification as a <dfn>pressure source sample</dfn>, a [=struct=]
+    consisting of the following [=struct/items=]:
+    <ul>
+      <li>
+        <dfn data-dfn-for="pressure source sample">data</dfn>: [=contributing
+        factors=] obtained from the underlying hardware or operating system.
+      </li>
+      <li>
+        <dfn data-dfn-for="pressure source sample">timestamp</dfn>: the
+        [=unsafe shared current time=] when [=pressure source sample/data=] was
+        obtained.
+        <aside class="note">
+          <p>
+            The purpose of [=pressure source sample/timestamp=] is to use the
+            same [=monotonic clock/unsafe current time=] for a sample across
+            all globals and invocations of the [=data collection=] algorithm
+            which are processing the same [=pressure source sample=].
+          </p>
+        </aside>
+      </li>
+    </ul>
+  </p>
   <p>
     A <dfn>platform collector</dfn> is an abstract interface responsible for
     obtaining telemetry samples from a [=pressure source=], translating them
@@ -1336,52 +1360,57 @@ <h3>Data Collection and Delivery</h3>
         <li>
           Let |state:PressureState| be null.
         </li>
+        <li>
+          Let |rawTimestamp| be null.
+        </li>
         <li>
           If |pressureSource| is a [=virtual pressure source=]:
           <ol>
             <li>
               Set |state| to |pressureSource|'s [=virtual pressure
-              source/pending sample=].
+              source/pending sample=]'s [=pending sample descriptor/state=].
             </li>
             <li>
               If |state| is null, abort these steps.
             </li>
+            <li>
+              Set |rawTimestamp| to |pressureSource|'s [=virtual pressure
+              source/pending sample=]'s [=pending sample
+              descriptor/timestamp=].
+            </li>
           </ol>
         </li>
         <li>
           Otherwise:
           <ol>
+            <li>
+              Let |sample| be |pressureSource|'s [=pressure source sample=].
+            </li>
             <li>
               Set |state| to an [=adjusted pressure state=] calculated from
-              |source| and any [=implementation-defined=] platform data related
-              to |source|.
+              |source| and |sample|'s [=pressure source sample/data=].
               <aside class="note">
                 <p>
-                  The data sample and the mapping between data sample and [=pressure states=]
-                  is [=implementation-defined=] and may use many different metrics. For instance,
-                  for CPU, it might consider processor frequency and utilization, as well
-                  as thermal conditions.
+                  The mapping between |sample|'s [=pressure source
+                  sample/data=] and [=pressure states=] is
+                  [=implementation-defined=] and may use many different
+                  metrics. For instance, for CPU, it might consider processor
+                  frequency and utilization, as well as thermal conditions.
                 </p>
               </aside>
             </li>
+            <li>
+              Set |rawTimestamp| to |sample|'s [=pressure source
+              sample/timestamp=].
+            </li>
           </ol>
         </li>
         <li>
           [=Assert=]: |state| is not null.
         </li>
         <li>
-          Let |timestamp| be a platform-specific timestamp converted in an [=implementation-defined=]
-          way to an [=monotonic clock/unsafe current time=] using the same [=monotonic clock=]
-          that is shared by [=environment settings object/time origins=].
-        <aside class="note">
-          The goal of this step is to ensure that a timestamp that may have been relative to
-          a different time origin is converted to a value that can be used in computations with
-          the same [=monotonic clock=] used by the operations described in [[HR-TIME]].
-        </aside>
-        </li>
-        <li>
-          Let |timeValue| be the [=relative high resolution time=] based on |timestamp| and
-          |relevantGlobal|.
+          Let |timeValue| be the [=relative high resolution time=] based on
+          |rawTimestamp| and |relevantGlobal|.
         </li>
         <li>
           [=list/For each=] |observer:PressureObserver| in |relevantGlobal|'s
@@ -1921,12 +1950,26 @@ <h2>
     state=] values directly instead of [=implementation-defined=] values that
     must be processed into [=pressure states=] by a [=platform collector=].
   </p>
+  <p>
+    A <dfn>pending sample descriptor</dfn> is a [=struct=] with the following
+    [=struct/items=]:
+    <ul>
+      <li>
+        <dfn data-dfn-for="pending sample descriptor">state</dfn>, a
+        {{PressureState}}.
+      </li>
+      <li>
+        <dfn data-dfn-for="pending sample descriptor">timestamp</dfn>, a
+        [=monotonic clock/unsafe current time=] from the [=monotonic clock=].
+      </li>
+    </ul>
+  </p>
   <p>
     Each [=virtual pressure source=] has:
     <ul>
       <li>
-        a <dfn data-dfn-for="virtual pressure source">pending sample</dfn> of
-        type {{PressureState}} or null, which is initially null.
+        a <dfn data-dfn-for="virtual pressure source">pending sample</dfn>,
+        which is a [=pending sample descriptor=] or null.
       </li>
       <li>
         a <dfn data-dfn-for="virtual pressure source">can provide samples
@@ -2161,7 +2204,7 @@ <h4>
   </table>
   <p>
     This [=extension command=] allows updating the state of a [=virtual pressure source=] by pushing
-    a new [=virtual pressure source/pending sample=].
+    a new [=pending sample descriptor=].
   </p>
   <aside class="note" data-cite="WEBDRIVER2">
     Additionally, the [=extension command=] can be used to check whether a source type is created
@@ -2230,7 +2273,10 @@ <h4>
       If |sample| is not of type {{PressureState}}, return [=error=] with [=error code|WebDriver error code=] [=invalid argument=].
     </li>
     <li>
-      Set |virtualPressureSource|'s [=virtual pressure source/pending sample=] to |sample|.
+      Set |virtualPressureSource|'s [=virtual pressure source/pending sample=]
+      to a new [=pending sample descriptor=] whose [=pending sample
+      descriptor/state=] is |sample| and [=pending sample
+      descriptor/timestamp=] is the [=unsafe shared current time=].
     </li>
     <li>
       In an [=implementation-defined=] way, make |virtualPressureSource|'s