[BUGFIX release] Fix uglification introduced bug with super wrapping.

We check to see if a function contains `_super` / `.call` / `.apply`
before attempting to super wrap a given method (this saves quite a bit
of extra super wrapping for functions that do not need it).
Unfortunately, a number of platforms that we support do not support
calling `func.toString()` so we attempt to detect this and fall back
to always super wrap everything mode.

We have roughly this code (from
[here](https://github.com/emberjs/ember.js/blob/b4718218dbe5ffe7736c485a594248b20977c621/packages/ember-metal/lib/utils.js#L257-L271))
to detect if we can call `toString()` and get the original source:

```javascript
  let sourceAvailable = (function() {
    return this;
  }).toString().indexOf('return this;') > -1;
```

This works perfectly for development builds, but unfortunately not
when minified.  Take a look at the minified source and you will see why:

```javascript
var e=function(){return this}.toString().indexOf("return this;")>-1;
```

Note that minifier has stripped the trailing semicolon from the function
body we are attempting to check against, but sadly our `indexOf` check
still contains the semicolon!

**tldr;** We super wrap every function in uglified builds.

---

This commit removes the trailing semicolon from the source check, and
adds a test that should hopefully allow us to detect if this is
accidentally reintroduced.

packages/ember-metal/lib/environment.js

@@ -26,6 +26,7 @@ if (hasDOM) {
     hasDOM: true,
     isChrome: !!window.chrome && !window.opera,
     isFirefox: typeof InstallTrigger !== 'undefined',
+    isPhantom: !!window.callPhantom,
     location: window.location,
     history: window.history,
     userAgent: window.navigator.userAgent,
@@ -36,6 +37,7 @@ if (hasDOM) {
     hasDOM: false,
     isChrome: false,
     isFirefox: false,
+    isPhantom: false,
     location: null,
     history: null,
     userAgent: 'Lynx (textmode)',

packages/ember-metal/lib/utils.js

@@ -254,10 +254,10 @@ export function guidFor(obj) {
 
 const HAS_SUPER_PATTERN = /\.(_super|call\(this|apply\(this)/;
 
-const checkHasSuper = (function () {
+export const checkHasSuper = (function () {
   let sourceAvailable = (function() {
     return this;
-  }).toString().indexOf('return this;') > -1;
+  }).toString().indexOf('return this') > -1;
 
   if (sourceAvailable) {
     return function checkHasSuper(func) {

packages/ember-metal/tests/utils_test.js

@@ -1,4 +1,5 @@
-import { inspect } from 'ember-metal/utils';
+import { inspect, checkHasSuper } from 'ember-metal/utils';
+import environment from 'ember-metal/environment';
 
 QUnit.module('Ember Metal Utils');
 
@@ -14,3 +15,12 @@ QUnit.test('inspect outputs the toString() representation of Symbols', function(
     expect(0);
   }
 });
+
+// Only run this test on browsers that we are certain should have function
+// source available.  This allows the test suite to continue to pass on other
+// platforms that correctly (for them) fall back to the "always wrap" code.
+if (environment.isPhantom || environment.isChrome || environment.isFirefox) {
+  QUnit.test('does not super wrap needlessly [GH #12462]', function(assert) {
+    assert.notOk(checkHasSuper(function() {}), 'empty function does not have super');
+  });
+}