Allow task pools to reason about transparency.

cc/raster/bitmap_tile_task_worker_pool.cc

Index: cc/raster/bitmap_tile_task_worker_pool.cc
diff --git a/cc/raster/bitmap_tile_task_worker_pool.cc b/cc/raster/bitmap_tile_task_worker_pool.cc
index 8c6513b189e15efc4a0a3babee42fbe9d6cbec41..034ad0f087b5554c317c121aefef8b8b8bbc19a8 100644
--- a/cc/raster/bitmap_tile_task_worker_pool.cc
+++ b/cc/raster/bitmap_tile_task_worker_pool.cc
@@ -179,12 +179,15 @@ void BitmapTileTaskWorkerPool::CheckForCompletedTasks() {
   completed_tasks_.clear();
 }
 
-ResourceFormat BitmapTileTaskWorkerPool::GetResourceFormat() const {
+ResourceFormat BitmapTileTaskWorkerPool::GetResourceFormat(
+    bool must_support_alpha) const {
   return resource_provider_->best_texture_format();
 }
 
-bool BitmapTileTaskWorkerPool::GetResourceRequiresSwizzle() const {
-  return !PlatformColor::SameComponentOrder(GetResourceFormat());
+bool BitmapTileTaskWorkerPool::GetResourceRequiresSwizzle(
+    bool must_support_alpha) const {
+  return !PlatformColor::SameComponentOrder(
+      GetResourceFormat(must_support_alpha));
 }
 
 scoped_ptr<RasterBuffer> BitmapTileTaskWorkerPool::AcquireBufferForRaster(