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

content/common/gpu/client/webgraphicscontext3d_command_buffer_impl.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/common/gpu/client/webgraphicscontext3d_command_buffer_impl.h"
 
 #include "third_party/khronos/GLES2/gl2.h"
 #ifndef GL_GLEXT_PROTOTYPES
 #define GL_GLEXT_PROTOTYPES 1
 #endif
@@ skipping 1527 matching lines @@
 void WebGraphicsContext3DCommandBufferImpl::signalSyncPoint(
     unsigned sync_point,
     WebGraphicsSyncPointCallback* callback) {
   // Take ownership of the callback.
   scoped_ptr<WebGraphicsSyncPointCallback> own_callback(callback);
   command_buffer_->SignalSyncPoint(
       sync_point,
       base::Bind(&SignalSyncPointCallback, base::Passed(&own_callback)));
 }
 
+void WebGraphicsContext3DCommandBufferImpl::signalQuery(
+    unsigned query,
+    WebGraphicsSyncPointCallback* callback) {
+  // Take ownership of the callback.
+  scoped_ptr<WebGraphicsSyncPointCallback> own_callback(callback);
+  // Flush any pending commands to make sure that the the query
+  // has actually been created/started before we try to attach
+  // a callback to it.
+  gl_->Flush();
+  command_buffer_->SignalQuery(
+      query,
+      base::Bind(&SignalSyncPointCallback, base::Passed(&own_callback)));
+}
+
 void WebGraphicsContext3DCommandBufferImpl::genMailboxCHROMIUM(
     WGC3Dbyte* name) {
   std::vector<gpu::Mailbox> names;
   if (command_buffer_->GenerateMailboxNames(1, &names))
     memcpy(name, names[0].name, GL_MAILBOX_SIZE_CHROMIUM);
   else
     synthesizeGLError(GL_OUT_OF_MEMORY);
 }
 
 DELEGATE_TO_GL_2(produceTextureCHROMIUM, ProduceTextureCHROMIUM,
@@ skipping 102 matching lines @@
 
 void WebGraphicsContext3DCommandBufferImpl::OnErrorMessage(
     const std::string& message, int id) {
   if (error_message_callback_) {
     WebKit::WebString str = WebKit::WebString::fromUTF8(message.c_str());
     error_message_callback_->onErrorMessage(str, id);
   }
 }
 
 }  // namespace content