Add srcObject attribute of type MediaStream to HTMLMediaElement.

third_party/WebKit/Source/core/html/HTMLMediaElement.h

Index: third_party/WebKit/Source/core/html/HTMLMediaElement.h
diff --git a/third_party/WebKit/Source/core/html/HTMLMediaElement.h b/third_party/WebKit/Source/core/html/HTMLMediaElement.h
index 2a0ec2e9f3a4f7dae2749d73f9c5738d08013f5e..51d0993488d4985c9d8cc5b03f2c0f6c4fcf69ba 100644
--- a/third_party/WebKit/Source/core/html/HTMLMediaElement.h
+++ b/third_party/WebKit/Source/core/html/HTMLMediaElement.h
@@ -108,6 +108,7 @@ public:
     // network state
     void setSrc(const AtomicString&);
     const KURL& currentSrc() const { return m_currentSrc; }
+    void setSrcObjectURL(const AtomicString&);

[philipj_slow, 2016/03/21 11:13:13]

Rather than using an object URL, can you look into something like
Source/platform/MediaProvider which wraps the MediaStream (and later other
types), with the isMediaStream()/getAsMediaStream() pattern that generated union
types have?

This class (maybe it has to be public/platform/WebMediaProvider) would be used
by FrameLoaderClientImpl::createWebMediaPlayer or
RenderFrameImpl::createMediaPlayer to create a WebMediaPlayerMS instance for the
MediaStream object.

[Guido Urdaneta, 2016/03/21 16:34:53]

Source/platform and public/platform cannot access MediaStream due to dependency
restrictions. Fortunately, this dependency problem has already been solved for
MediaStreams with the MediaStreamDescriptor class in Source/platform.

The main difficulty I see of not using the URL is that all the code from
HTMLMediaElement to the creation of the WebMediaPlayer uses the URL, and it's in
the lowest layer where the MediaStreamDescriptor is obtained from the URL.

I think we would need alternative non-URL versions of at least
HTMLMediaElement::loadResource(), HTMLMediaElement::startPlayerLoad(),
FrameLoaderClientImpl::createWebMediaPlayer(), and
RenderFrameImpl::createMediaPlayer(). At first sight, it looks like a lot of
work. Of course, I'm not familiar with HTMLMediaElement code, so maybe there is
a way to do it without duplicating much code.

[philipj_slow, 2016/03/22 16:06:54]

Just judging by include rules, maybe public/web/WebMediaProvider.h +
Source/web/WebMediaProvider.cpp would work?

As for HTMLMediaElement processing, the nicest thing would be an entry point
that matches
https://html.spec.whatwg.org/multipage/embedded-content.html#concept-media-lo...
so that one can be confident that the implementation matches the spec. One idea
would be to let the WebMediaProvider represent both URLs and all kinds of
srcObjects and to use that throughout. Do you think that could work?

[Guido Urdaneta, 2016/03/24 14:38:44]

I went for the URL+srcObject approach. I called the class
public/platform/WebMediaElementSource. I did not use WebMediaProvider since the
spec uses that term for the non-URL case. I'm open to naming suggestions though
:)

I couldn't exactly match
https://html.spec.whatwg.org/multipage/embedded-content.html#concept-media-lo...
 because that logic seems to be split across HTMLMediaElement and the various
WebMediaPlayers. Intead, I left the current loading logic practically
unmodified. Just ignoring URL checks when it's an srcObject.

Please let me know what you think.

 
     enum NetworkState { NETWORK_EMPTY, NETWORK_IDLE, NETWORK_LOADING, NETWORK_NO_SOURCE };
     NetworkState getNetworkState() const;
@@ -355,6 +356,9 @@ private:
     void setPlayerPreload();
     WebMediaPlayer::LoadType loadType() const;
     void scheduleNextSourceChild();
+    void loadSourceFromObject();
+    void loadSourceFromAttribute();
+    void loadSourceFromURL(const AtomicString&);
     void loadNextSourceChild();
     void clearMediaPlayer();
     void clearMediaPlayerAndAudioSourceProviderClientWithoutLocking();
@@ -499,10 +503,11 @@ private:
     double m_defaultPlaybackStartPosition;
 
     // Loading state.
-    enum LoadState { WaitingForSource, LoadingFromSrcAttr, LoadingFromSourceElement };
+    enum LoadState { WaitingForSource, LoadingFromSrcObject, LoadingFromSrcAttr, LoadingFromSourceElement };
     LoadState m_loadState;
     RefPtrWillBeMember<HTMLSourceElement> m_currentSourceNode;
     RefPtrWillBeMember<Node> m_nextChildNodeToConsider;
+    AtomicString m_srcObjectURL;
 
     // "Deferred loading" state (for preload=none).
     enum DeferredLoadState {