Bug 1576703 - Update cbindgen. r=boris

This cleans up the pattern of "Use a private dtor so that the helper functions
do the right thing" by enabling it everywhere using:

  mozilla/cbindgen#377

It also caught some uninitialized value issues.

I think they're mostly harmless since we zero-initialize our structs:

https://searchfox.org/mozilla-central/rev/325c1a707819602feff736f129cb36055ba6d94f/servo/components/style/properties/gecko.mako.rs#632

And since we override the clip rect, which is the other bit of code that was
failing to build with this change.

Differential Revision: https://phabricator.services.mozilla.com/D43491

UltraBlame original commit: 6c3f50c6f6662291139bc292fb9dd77aa64331ee

build/moz.configure/bindgen.configure

@@ -15,7 +15,7 @@ option(env='CBINDGEN', nargs=1, when=cbindgen_is_needed,
 def check_cbindgen_version(cbindgen, fatal=False):
     log.debug("trying cbindgen: %s" % cbindgen)
 
-    cbindgen_min_version = Version('0.9.0')
+    cbindgen_min_version = Version('0.9.1')
 
     # cbindgen x.y.z
     version = Version(check_cmd_output(cbindgen, '--version').strip().split(" ")[1])

layout/style/FontFace.cpp

@@ -629,7 +629,7 @@ Maybe<StyleComputedFontStretchRange> FontFace::GetFontStretch() const {
 }
 
 Maybe<StyleComputedFontStyleDescriptor> FontFace::GetFontStyle() const {
-  StyleComputedFontStyleDescriptor descriptor;
+  auto descriptor = StyleComputedFontStyleDescriptor::Normal();
   if (!Servo_FontFaceRule_GetFontStyle(GetData(), &descriptor)) {
     return Nothing();
   }

layout/style/FontFaceSet.cpp

@@ -205,7 +205,7 @@ void FontFaceSet::ParseFontShorthandForMatching(
     const nsAString& aFont, RefPtr<SharedFontList>& aFamilyList,
     FontWeight& aWeight, FontStretch& aStretch, FontSlantStyle& aStyle,
     ErrorResult& aRv) {
-  StyleComputedFontStyleDescriptor style;
+  auto style = StyleComputedFontStyleDescriptor::Normal();
   float stretch;
   float weight;