Remove the always-enabled Media from RuntimeEnabledFeatures

third_party/WebKit/Source/bindings/IDLExtendedAttributes.md

 # Blink IDL Extended Attributes
 
 [TOC]
 
 ## Introduction
 
 The main interest in extended attributes are their _semantics_: Blink implements many more extended attributes than the Web IDL standard, to specify various behavior.
 
 The authoritative list of allowed extended attributes and values is [bindings/IDLExtendedAttributes.txt](https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit/Source/bindings/IDLExtendedAttributes.txt). This is complete but not necessarily precise (there may be unused extended attributes or values), since validation is run on build, but coverage isn't checked.
 
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 `[ReflectOnly=<list>]` should be used if the specification for a reflected IDL attribute says it is _"limited to only known values"_.
 
 ### [RuntimeEnabled] _(i, m, a, c)_
 
 Summary: `[RuntimeEnabled]` wraps the generated code with `if (RuntimeEnabledFeatures::FeatureNameEnabled) { ...code... }`.
 
 Usage: `[RuntimeEnabled=FeatureName]`. FeatureName must be included in [RuntimeEnabledFeatures.in](https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit/Source/platform/RuntimeEnabledFeatures.in).
 
 ```webidl
 [
-    RuntimeEnabled=Media,
-] interface HTMLAudioElement : HTMLMediaElement {};
+    RuntimeEnabled=MediaSession
+] interface MediaSession { ... };
 ```
 
 Only when the feature is enabled at runtime (using a command line flag, for example, or when it is enabled only in certain platforms), the binding would be exposed to the web.
 
 `[RuntimeEnabled]` _cannot_ be applied to arguments, as this changes signatures and method resolution and is both very confusing to reason about and implement. For example, what does it mean to mark a _required_ argument as `[RuntimeEnabled]`? You probably want to apply it only to optional arguments, which are equivalent to overloads. Thus instead apply `[RuntimeEnabled]` to the _method_, generally splitting a method in two. For example, instead of:
 
 ```webidl
 foo(long x, `[RuntimeEnabled=FeatureName]` optional long y); // Don't do this!
 ```
 
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