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.

layout/base/nsLayoutUtils.cpp

@@ -7242,9 +7242,11 @@ nsLayoutUtils::SurfaceFromElement(HTMLVideoElement* aElement,
     (aSurfaceFlags & SFE_PREFER_NO_PREMULTIPLY_ALPHA) == 0,
     "We can't support non-premultiplied alpha for video!");
 
+#ifdef MOZ_EME
   if (aElement->ContainsRestrictedContent()) {
     return result;
   }
+#endif
 
   uint16_t readyState;
   if (NS_SUCCEEDED(aElement->GetReadyState(&readyState)) &&