Perform glReadPixels with PBOs in the gpu, if PBOs are available.

cc/resources/sync_point_helper.cc

Index: cc/resources/sync_point_helper.cc
diff --git a/cc/resources/sync_point_helper.cc b/cc/resources/sync_point_helper.cc
index f4eea70eb9d09d3670b46cd14ff244a7404fd319..f5822a41ae98356c5afa28f2be929db80a55ae63 100644
--- a/cc/resources/sync_point_helper.cc
+++ b/cc/resources/sync_point_helper.cc
@@ -34,4 +34,15 @@ void SyncPointHelper::SignalSyncPoint(
   context3d->signalSyncPoint(sync_point, callback_class);
 }
 
+void SyncPointHelper::SignalQuery(
+    WebKit::WebGraphicsContext3D* context3d,
+    WebKit::WebGLId query,
+    const base::Closure& closure) {
+  SignalSyncPointCallbackClass* callback_class =
+      new SignalSyncPointCallbackClass(closure);
+
+  // Pass ownership of the CallbackClass to WebGraphicsContext3D.
+  context3d->signalQuery(query, callback_class);
+}
+
 }  // namespace cc