Use explicit flush for ArcVideoAccelerator.

components/arc/common/video_accelerator.mojom

Index: components/arc/common/video_accelerator.mojom
diff --git a/components/arc/common/video_accelerator.mojom b/components/arc/common/video_accelerator.mojom
index d20a2360b17f10ecb74acac23d5b47be888f16dd..d6b0bd589faf455997390ad84c1207729e85ae3f 100644
--- a/components/arc/common/video_accelerator.mojom
+++ b/components/arc/common/video_accelerator.mojom
@@ -19,11 +19,6 @@ enum PortType {
   PORT_OUTPUT = 1,
 };
 
-[Extensible]
-enum BufferFlag {
-  BUFFER_FLAG_EOS = 1,
-};
-
 struct BufferMetadata {
   int64 timestamp;  // in microseconds
   uint32 flags;
@@ -68,6 +63,8 @@ interface VideoAcceleratorService {
   SetNumberOfOutputBuffers@4(uint32 number);
 
   Reset@5();
+
+  Flush@6();

[dcheng, 2016/05/07 06:18:11]

Out of curiosity, how come we don't do something like Flush@6() => (), so the
caller can just wait for the return callback?

[Owen Lin, 2016/05/09 07:04:41]

Just make it similar to the VDA interface:

https://code.google.com/p/chromium/codesearch#chromium/src/media/video/video_...

[dcheng, 2016/05/09 21:22:00]

Wouldn't the code be simpler though if we just used the appropriate mojo
primitives? Is there some advantage to having two separate interfaces for one
logical call that I'm missing?

[Owen Lin, 2016/05/10 08:26:33]

I think you're right that we can use mojo primitives for Flush() -->
onFlushDone() or Reset()--> onResetDone().

But I don't see much benefits/difference. We still need the interface for error
handling and other callbacks. Adding these completion callbacks to the interface
seems a better idea. Otherwise, in Chromium side, we need to keep those
callbacks and invoke them when we are notified by
VDA::Client::Notify(Flush|Reset)Done().

In addition, that also makes people who are familiar with VDA easy to
match/understand the code.

The question makes me to think why VDA was not designed as using
Flush(base::Closure callback). But I don't see strong reason/benefit to change
it.

 };
 
 interface VideoAcceleratorServiceClient {
@@ -88,4 +85,6 @@ interface VideoAcceleratorServiceClient {
   OnResetDone@3();
 
   OnOutputFormatChanged@4(VideoFormat format);
+
+  OnFlushDone@5();
 };