Don't build EME-specific subroutines without EME.

- Checks for restricted or encrypted content
- Dispatching 'encrypted' events
- Dispatching 'key needed' events
- HTML Media Element media keys system
- EME telemetry
- HTML Media Element EME API

This is the main bulk for #26, isolating EME-specific code.

dom/media/MediaDecoderOwner.h

@@ -143,11 +143,13 @@ public:
   // reference to the decoder to prevent further calls into the decoder.
   virtual void NotifyXPCOMShutdown() = 0;
 
+#ifdef MOZ_EME
   // Dispatches a "encrypted" event to the HTMLMediaElement, with the
   // provided init data. Actual dispatch may be delayed until HAVE_METADATA.
   // Main thread only.
   virtual void DispatchEncrypted(const nsTArray<uint8_t>& aInitData,
                                  const nsAString& aInitDataType) = 0;
+#endif
 };
 
 } // namespace mozilla