cc: Support on demand raster with ganesh

cc/resources/raster_worker_pool.cc

 // Copyright 2013 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/resources/raster_worker_pool.h"
 
 #include <algorithm>
 
 #include "base/atomic_sequence_num.h"
 #include "base/debug/trace_event_synthetic_delay.h"
@@ skipping 28 matching lines @@
               this,
               base::StringPrintf("CompositorRasterWorker%u",
                                  static_cast<unsigned>(workers_.size() + 1))
                   .c_str()));
       worker->Start();
 #if defined(OS_ANDROID) || defined(OS_LINUX)
       worker->SetThreadPriority(base::kThreadPriority_Background);
 #endif
       workers_.push_back(worker.Pass());
     }
-
-    // Use index 0 for origin thread.
-    current_tls_.Set(new ThreadLocalState(0));
   }
 
   virtual ~RasterTaskGraphRunner() { NOTREACHED(); }
 
   size_t GetPictureCloneIndexForCurrentThread() {
-    return current_tls_.Get()->picture_clone_index;
+    // Use index 0 for origin thread and any unknown threads.

[reveman, 2014/06/20 18:44:19]

nit: "Use index 0 if called on non-raster thread."

+    ThreadLocalState* thread_local_state = current_tls_.Get();
+    return thread_local_state ? current_tls_.Get()->picture_clone_index : 0;
   }
 
  private:
   struct ThreadLocalState {
     explicit ThreadLocalState(size_t picture_clone_index)
         : picture_clone_index(picture_clone_index) {}
 
     size_t picture_clone_index;
   };
 
@@ skipping 214 matching lines @@
     if (decode_it == graph->nodes.end())
       InsertNodeForTask(graph, decode_task, priority, 0u);
 
     graph->edges.push_back(TaskGraph::Edge(decode_task, raster_task));
   }
 
   InsertNodeForTask(graph, raster_task, priority, dependencies);
 }
 
 }  // namespace cc