Revert of cc: Remove WorkerPool class and instead use TaskGraphRunner directly.

cc/trees/layer_tree_host_impl.cc

 // Copyright 2011 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 "cc/trees/layer_tree_host_impl.h"
 
 #include <algorithm>
 #include <limits>
 
 #include "base/basictypes.h"
@@ skipping 88 matching lines @@
 }
 
 size_t GetMaxRasterTasksUsageBytes(cc::ContextProvider* context_provider) {
   // Transfer-buffer/raster-tasks limits are different but related. We make
   // equal here, as this is ideal when using transfer buffers. When not using
   // transfer buffers we should still limit raster to something similar, to
   // preserve caching behavior (and limit memory waste when priorities change).
   return GetMaxTransferBufferUsageBytes(context_provider);
 }
 
-unsigned GetMapImageTextureTarget(cc::ContextProvider* context_provider) {
+GLenum GetMapImageTextureTarget(cc::ContextProvider* context_provider) {
   if (!context_provider)
     return GL_TEXTURE_2D;
 
   // TODO(reveman): Determine if GL_TEXTURE_EXTERNAL_OES works well on
   // Android before we enable this. crbug.com/322780
 #if !defined(OS_ANDROID)
   if (context_provider->ContextCapabilities().gpu.egl_image_external)
     return GL_TEXTURE_EXTERNAL_OES;
   if (context_provider->ContextCapabilities().gpu.texture_rectangle)
     return GL_TEXTURE_RECTANGLE_ARB;
@@ skipping 2801 matching lines @@
   swap_promise_monitor_.erase(monitor);
 }
 
 void LayerTreeHostImpl::NotifySwapPromiseMonitorsOfSetNeedsRedraw() {
   std::set<SwapPromiseMonitor*>::iterator it = swap_promise_monitor_.begin();
   for (; it != swap_promise_monitor_.end(); it++)
     (*it)->OnSetNeedsRedrawOnImpl();
 }
 
 }  // namespace cc