Don't require VDAs to return all PictureBuffers at once.

media/video/video_decode_accelerator.h

Index: media/video/video_decode_accelerator.h
diff --git a/media/video/video_decode_accelerator.h b/media/video/video_decode_accelerator.h
index e2bcdf64855fdf3455fc0a3b73ae2b59c2e928e6..71c76db9e30fb0c30bd0b66c1e3176292d3db707 100644
--- a/media/video/video_decode_accelerator.h
+++ b/media/video/video_decode_accelerator.h
@@ -34,6 +34,22 @@ class MEDIA_EXPORT VideoDecodeAccelerator {
   };
   using SupportedProfiles = std::vector<SupportedProfile>;
 
+  struct MEDIA_EXPORT Capabilities {
+    Capabilities();
+    ~Capabilities();
+    // Flags that can be associated with a VDA.
+    enum Flags {
+      NO_FLAGS = 0,
+
+      // If set, then the VDA makes no guarantees that it won't stall before
+      // sending all the picture buffers to the client via PictureReady.
+      CAN_STALL_ANY_TIME = 1 << 0,

[Pawel Osciak, 2015/12/05 00:18:55]

My feeling is that "stall" is a very specific term that a person not familiar
with how our media pipeline works will likely not understand. Actually, I'm
still not sure I understand this fully myself. "Any time" also feels quite
confusing to me, what does it really tell us?

I'd really appreciate a precise explanation here if possible please. For example
(and please correct this if this is wrong, I am not sure if I am understanding
"stall" in this context correctly either):

"A stall happens when a VDA does not return some or all decoded and ready to be
displayed pictures via PictureReady() to the client, even though it is expected
to. In that case... [...explanation show should the client behave then...]"

Thanks.

[liberato (no reviews please), 2015/12/07 19:04:40]

i agree that it is rather specific.  i chose the name to match
CanReadWithoutStalling.  the problem is that it isn't exactly the right word
there, either.  it is more "CanReadWithoutMaybeDeadlocking" -- nobody actually
guarantees that the decoded frames are available immediately, only that they
will become available if one sends enough input and waits long enough.

i've rewritten the comment.

+    };
+
+    SupportedProfiles supported_profiles;
+    Flags flags;
+  };
+
   // Enumeration of potential errors generated by the API.
   // Note: Keep these in sync with PP_VideoDecodeError_Dev. Also do not
   // rearrange, reuse or remove values as they are used for gathering UMA