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

gpu/command_buffer/service/query_manager.cc

Index: gpu/command_buffer/service/query_manager.cc
diff --git a/gpu/command_buffer/service/query_manager.cc b/gpu/command_buffer/service/query_manager.cc
index 8d85cffc033134d236bd14da66b26b35d7a47c16..af211782fab19fc828cf2c891ab56fd640fb2bda 100644
--- a/gpu/command_buffer/service/query_manager.cc
+++ b/gpu/command_buffer/service/query_manager.cc
@@ -195,6 +195,8 @@ class AsyncPixelTransfersCompletedQuery
     base::subtle::MemoryBarrier();
     sync->process_count = submit_count;
   }
+  void MarkAsCompletedStage1(
+      uint32 submit_count, const AsyncMemoryParams& mem_params);
 };
 
 AsyncPixelTransfersCompletedQuery::AsyncPixelTransfersCompletedQuery(
@@ -218,6 +220,16 @@ bool AsyncPixelTransfersCompletedQuery::End(uint32 submit_count) {
   mem_params.shm_data_offset = shm_offset();
   mem_params.shm_data_size = sizeof(QuerySync);
 
+  manager()->decoder()->WaitForReadPixels(
+      base::Bind(&AsyncPixelTransfersCompletedQuery::MarkAsCompletedStage1,
+                 this, submit_count, mem_params));
+  return AddToPendingTransferQueue(submit_count);
+}
+
+void AsyncPixelTransfersCompletedQuery::MarkAsCompletedStage1(
+    uint32 submit_count,
+    const AsyncMemoryParams& mem_params) {
+
   // Ask AsyncPixelTransferDelegate to run completion callback after all
   // previous async transfers are done. No guarantee that callback is run
   // on the current thread.
@@ -225,8 +237,6 @@ bool AsyncPixelTransfersCompletedQuery::End(uint32 submit_count) {
       mem_params,
       base::Bind(AsyncPixelTransfersCompletedQuery::MarkAsCompletedThreadSafe,
                  submit_count));
-
-  return AddToPendingTransferQueue(submit_count);
 }
 
 bool AsyncPixelTransfersCompletedQuery::Process() {