gpu: Add sync token dependencies to flush metadata.

gpu/gles2_conform_support/egl/context.cc

Index: gpu/gles2_conform_support/egl/context.cc
diff --git a/gpu/gles2_conform_support/egl/context.cc b/gpu/gles2_conform_support/egl/context.cc
index 6b71251858fbd2b26af45b92122645c38fbb2309..c5036f9b0cdcc5dc07bca8286ae499c89d37e9d3 100644
--- a/gpu/gles2_conform_support/egl/context.cc
+++ b/gpu/gles2_conform_support/egl/context.cc
@@ -223,7 +223,9 @@ void Context::SignalSyncToken(const gpu::SyncToken& sync_token,
   NOTIMPLEMENTED();
 }
 
-bool Context::CanWaitUnverifiedSyncToken(const gpu::SyncToken* sync_token) {
+void Context::WaitSyncToken(const gpu::SyncToken& sync_token) {}

[dcheng, 2017/03/14 06:53:03]

Is this a NOTIMPLEMENTED kind of thing?

[sunnyps, 2017/03/15 00:03:08]

No, GLES2Implementation might call this. I don't know if WaitSyncToken is ever
called in this configuration, but it's OK to have a NOP implementation for this
method.

Maybe this method should be renamed? piman@ WDYT?

[piman, 2017/03/15 00:30:14]

It could be named something like WaitSyncTokenHint to indicate that it's a hint,
that can be used for scheduling, but doesn't have semantic meaning otherwise, so
it's ok to have it do nothing in some implementations?

[sunnyps, 2017/03/15 00:56:11]

Done.

+
+bool Context::CanWaitUnverifiedSyncToken(const gpu::SyncToken& sync_token) {
   return false;
 }