MSE: Start letting SourceBuffer begin to do initialization segment received algorithm

public/platform/WebSourceBuffer.h

Index: public/platform/WebSourceBuffer.h
diff --git a/public/platform/WebSourceBuffer.h b/public/platform/WebSourceBuffer.h
index 1f34a0c52ab9696ab3baf3b5f732cda54e8c0139..e9349fb3000ed1be87f170b3c588d2f21253a188 100644
--- a/public/platform/WebSourceBuffer.h
+++ b/public/platform/WebSourceBuffer.h
@@ -35,6 +35,8 @@
 
 namespace blink {
 
+class WebSourceBufferClient;
+
 class WebSourceBuffer {
 public:
     enum AppendMode {
@@ -43,6 +45,13 @@ public:
     };
 
     virtual ~WebSourceBuffer() { }
+
+    // This will only be called once and only with a valid pointer.

[philipj_slow, 2014/09/11 13:38:32]

Maybe say that it's never null, since valid is a bit vague and could mean just
not stale?

[wolenetz, 2014/09/11 21:41:17]

Done.

+    virtual void setClient(WebSourceBufferClient*)
+    {
+        // FIXME: Remove default implementation once Chromium impl lands.
+    }
+
     virtual bool setMode(AppendMode) = 0;
     virtual WebTimeRanges buffered() = 0;
 
@@ -60,6 +69,8 @@ public:
     // Set presentation timestamp for the end of append window.
     virtual void setAppendWindowEnd(double) = 0;
 
+    // The client passed to setClient() should never be called after this method

[philipj_slow, 2014/09/11 13:38:32]

I don't understand this comment. Does setClient() transfer ownership of the
WebSourceBufferClient to the WebSourceBuffer, but one is allowed to borrow a
reference until the removedFromMediaSource() call?

[wolenetz, 2014/09/11 21:41:17]

I've clarified this a bit more. I'm trying to indicate that there is no
ownership of the WebSourceBufferClient transferred to the WebSourceBuffer by
setClient(). setClient() passes a raw pointer. The WebSourceBuffer should not
use this raw pointer after removedFromMediaSource() is called; the pointer is
only 'valid' between setClient() and removedFromMediaSource(). WebSourceBuffer
does not own the client object.

[philipj_slow, 2014/09/12 08:45:28]

That's simple enough, and the updated comments are great, thanks!

+    // is called.
     virtual void removedFromMediaSource() = 0;
 };