Implement "Key Presence" step in "Encrypted Block Encounted" algorithm in EME.

media/base/decryptor.h

Index: media/base/decryptor.h
diff --git a/media/base/decryptor.h b/media/base/decryptor.h
index 56696695037a8ce1efba475b67552d6078bcabfe..537871ac293484eaf13fe3b5d9120ce2d8d053c5 100644
--- a/media/base/decryptor.h
+++ b/media/base/decryptor.h
@@ -20,7 +20,7 @@ class DecoderBuffer;
 // All public methods other than Decrypt() will be called on the renderer
 // thread. Therefore, these calls should be fast and nonblocking, with key
 // events fired asynchronously. Decrypt() will be called on the (video/audio)
-// decoder thread synchronously.
+// decoder thread.
 class MEDIA_EXPORT Decryptor {
  public:
   enum KeyError {
@@ -78,6 +78,9 @@ class MEDIA_EXPORT Decryptor {
   virtual void Decrypt(const scoped_refptr<DecoderBuffer>& encrypted,
                        const DecryptCB& decrypt_cb) = 0;
 
+  // Stops the decryptor and fires any pending DecryptCB immediately.

[scherkus (not reviewing), 2012/08/02 18:05:32]

fires the cb with what result?

[xhwang, 2012/08/03 20:08:10]

Done.

+  virtual void Stop() = 0;
+
  private:
   DISALLOW_COPY_AND_ASSIGN(Decryptor);
 };