Make sure Ppapi compositor layer resources are synchronized.

BUG=514815, 581951

Review URL: https://codereview.chromium.org/1641323002

Cr-Commit-Position: refs/heads/master@{#372232}

ppapi/proxy/compositor_layer_resource.cc

@@ -178,9 +178,8 @@ int32_t CompositorLayerResource::SetTexture(
   data_.texture->source_rect.size = source_size_;
 
   const GLuint64 fence_sync = gl->InsertFenceSyncCHROMIUM();
-  gl->OrderingBarrierCHROMIUM();
-  gl->GenUnverifiedSyncTokenCHROMIUM(fence_sync,
-                                     data_.texture->sync_token.GetData());
+  gl->ShallowFlushCHROMIUM();
+  gl->GenSyncTokenCHROMIUM(fence_sync, data_.texture->sync_token.GetData());
 
   // If the PP_Resource of this layer is released by the plugin, the
   // release_callback will be aborted immediately, but the texture or image