cc: Do bitmap conversion for RasterBuffer in the worker thread.

cc/resources/pixel_buffer_raster_worker_pool.cc

Index: cc/resources/pixel_buffer_raster_worker_pool.cc
diff --git a/cc/resources/pixel_buffer_raster_worker_pool.cc b/cc/resources/pixel_buffer_raster_worker_pool.cc
index f98779ccda77966f69fe3c19b6132deab8a8acec..b5faecebb4c61a7714ef33b201490f52910285ea 100644
--- a/cc/resources/pixel_buffer_raster_worker_pool.cc
+++ b/cc/resources/pixel_buffer_raster_worker_pool.cc
@@ -267,8 +267,7 @@ RasterBuffer* PixelBufferRasterWorkerPool::AcquireBufferForRaster(
                       raster_task_states_.end(),
                       RasterTaskState::TaskComparator(task)) !=
          raster_task_states_.end());
-  resource_provider_->AcquirePixelRasterBuffer(task->resource()->id());
-  return resource_provider_->MapPixelRasterBuffer(task->resource()->id());
+  return resource_provider_->AcquirePixelRasterBuffer(task->resource()->id());
 }
 
 void PixelBufferRasterWorkerPool::ReleaseBufferForRaster(RasterTask* task) {
@@ -683,14 +682,10 @@ void PixelBufferRasterWorkerPool::CheckForCompletedRasterizerTasks() {
     RasterTaskState& state = *state_it;
     DCHECK_EQ(RasterTaskState::SCHEDULED, state.type);
 
-    // Balanced with MapPixelRasterBuffer() call in AcquireBufferForRaster().
-    bool content_has_changed = resource_provider_->UnmapPixelRasterBuffer(
-        raster_task->resource()->id());
-
     // |content_has_changed| can be false as result of task being canceled or
     // task implementation deciding not to modify bitmap (ie. analysis of raster
     // commands detected content as a solid color).
-    if (!content_has_changed) {
+    if (!raster_task->content_has_changed()) {

[reveman, 2014/08/13 19:19:49]

Let's keep things simple and remove all this conditional "contents have changed"
code from here. This is currently here to avoid an upload when analysis
determined the tile to be solid. We can handle that in BeginSetPixels instead
and avoid an upload at that level. This will make this code much cleaner without
having a real impact on performance.

[auygun, 2014/08/14 10:35:42]

Unittests assume that BeginSetPixels always uploads. Also
PixelBufferRasterWorkerPool still needs to know if any uploads has been
performed since last flush. So I'm adding TryBeginSetPixels which calls
BeginSetPixels if raster bitmap was modified.

[reveman, 2014/08/14 12:26:36]

Can we instead fix the unit tests and have PixelBufferRasterWorkerPool assume
that all BeginSetPixels calls result in an upload? I think that would be much
cleaner. There's already the case that BeginSetPixels might not actually perform
an upload if the context is lost.

[auygun, 2014/08/15 09:20:40]

Done.

       raster_task->WillComplete();
       raster_task->CompleteOnOriginThread(this);
       raster_task->DidComplete();