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..dab3a5861be6b3344abe2c6175392fda58e696de 100644
--- a/ppapi/proxy/ppapi_command_buffer_proxy.cc
+++ b/ppapi/proxy/ppapi_command_buffer_proxy.cc
@@ -214,8 +214,13 @@ void PpapiCommandBufferProxy::SignalSyncToken(const gpu::SyncToken& sync_token,
   NOTIMPLEMENTED();
 }
 
+void PpapiCommandBufferProxy::WaitSyncTokenHint(
+    const gpu::SyncToken& sync_token) {
+  // TODO(sunnyps): Forward sync token dependency hints to the renderer.
+}
+
 bool PpapiCommandBufferProxy::CanWaitUnverifiedSyncToken(
-    const gpu::SyncToken* sync_token) {
+    const gpu::SyncToken& sync_token) {
   return false;
 }