gpu: Add sync token dependencies to flush metadata.

ppapi/proxy/ppapi_command_buffer_proxy.cc

Index: ppapi/proxy/ppapi_command_buffer_proxy.cc
diff --git a/ppapi/proxy/ppapi_command_buffer_proxy.cc b/ppapi/proxy/ppapi_command_buffer_proxy.cc
index 8a5d0622a707e83a0a549fe310aae6717a62b88f..2ba3e8114a29fe7be245da8aa498d42f33c5bc05 100644
--- a/ppapi/proxy/ppapi_command_buffer_proxy.cc
+++ b/ppapi/proxy/ppapi_command_buffer_proxy.cc
@@ -214,8 +214,10 @@ void PpapiCommandBufferProxy::SignalSyncToken(const gpu::SyncToken& sync_token,
   NOTIMPLEMENTED();
 }
 
+void PpapiCommandBufferProxy::WaitSyncToken(const gpu::SyncToken& sync_token) {}

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

Is this a NOTIMPLEMENTED() kind of thing as well?

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

No, pepper can wait on sync tokens and GLES2Implementation will call this method
in that case. We could annotate pepper's flushes with sync tokens like we do for
command buffer proxy but it's optional.

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

We could add a TODO to forward this to the renderer, but it's so seldom used
that I think it's ok to punt for now.

[sunnyps, 2017/03/15 00:56:12]

Done.

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