Allow task pools to reason about transparency.

cc/raster/zero_copy_tile_task_worker_pool.cc

Index: cc/raster/zero_copy_tile_task_worker_pool.cc
diff --git a/cc/raster/zero_copy_tile_task_worker_pool.cc b/cc/raster/zero_copy_tile_task_worker_pool.cc
index 2e3dca1407f3358802bbd612554bf5f22ea46c4d..542dc253691560d640da6eeb34f576ac8803cf54 100644
--- a/cc/raster/zero_copy_tile_task_worker_pool.cc
+++ b/cc/raster/zero_copy_tile_task_worker_pool.cc
@@ -179,12 +179,16 @@ void ZeroCopyTileTaskWorkerPool::CheckForCompletedTasks() {
   completed_tasks_.clear();
 }
 
-ResourceFormat ZeroCopyTileTaskWorkerPool::GetResourceFormat() const {
-  return resource_provider_->memory_efficient_texture_format();
+ResourceFormat ZeroCopyTileTaskWorkerPool::GetResourceFormat(
+    bool must_support_alpha) const {
+  return resource_provider_->memory_efficient_texture_format(
+      must_support_alpha);
 }
 
-bool ZeroCopyTileTaskWorkerPool::GetResourceRequiresSwizzle() const {
-  return !PlatformColor::SameComponentOrder(GetResourceFormat());
+bool ZeroCopyTileTaskWorkerPool::GetResourceRequiresSwizzle(
+    bool must_support_alpha) const {
+  return !PlatformColor::SameComponentOrder(
+      GetResourceFormat(must_support_alpha));
 }
 
 scoped_ptr<RasterBuffer> ZeroCopyTileTaskWorkerPool::AcquireBufferForRaster(