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

webkit/common/gpu/webgraphicscontext3d_in_process_command_buffer_impl.cc

Index: webkit/common/gpu/webgraphicscontext3d_in_process_command_buffer_impl.cc
diff --git a/webkit/common/gpu/webgraphicscontext3d_in_process_command_buffer_impl.cc b/webkit/common/gpu/webgraphicscontext3d_in_process_command_buffer_impl.cc
index 84880201db5845066804782381fb760d1a5bf137..612443c7d66aab0b06c947737b787a3b3fbc61a3 100644
--- a/webkit/common/gpu/webgraphicscontext3d_in_process_command_buffer_impl.cc
+++ b/webkit/common/gpu/webgraphicscontext3d_in_process_command_buffer_impl.cc
@@ -1963,6 +1963,16 @@ void WebGraphicsContext3DInProcessCommandBufferImpl::signalSyncPoint(
   shallowFlushCHROMIUM();
 }
 
+void WebGraphicsContext3DInProcessCommandBufferImpl::signalQuery(
+    unsigned query,
+    WebGraphicsSyncPointCallback* callback) {
+  finish();
+  // Take ownership of the callback.
+  context_->SetSignalSyncPointCallback(make_scoped_ptr(callback));
+  // Stick something in the command buffer.
+  shallowFlushCHROMIUM();
+}
+
 void WebGraphicsContext3DInProcessCommandBufferImpl::loseContextCHROMIUM(
     WGC3Denum current, WGC3Denum other) {
   context_->LoseContext(current, other);