Allow task pools to reason about transparency.

cc/raster/tile_task_runner.h

Index: cc/raster/tile_task_runner.h
diff --git a/cc/raster/tile_task_runner.h b/cc/raster/tile_task_runner.h
index 64c72f0235ec638905dabb8a8236e383bf18b976..103da1fa275522ddedb57c3ca5330574e933bbcd 100644
--- a/cc/raster/tile_task_runner.h
+++ b/cc/raster/tile_task_runner.h
@@ -149,10 +149,10 @@ class CC_EXPORT TileTaskRunner {
   virtual void CheckForCompletedTasks() = 0;
 
   // Returns the format to use for the tiles.
-  virtual ResourceFormat GetResourceFormat() const = 0;
+  virtual ResourceFormat GetResourceFormat(bool must_support_alpha) const = 0;

[reveman, 2015/09/22 14:18:49]

This looks good for now. What do you think about adding something like this in
the future:

enum ResourceFormatDescription {
  COLOR,
  COLOR_AND_ALPHA,
  UNCOMPRESSED_COLOR_AND_ALPHA
};

[christiank, 2015/09/23 12:29:11]

I like it! Much better than the old "two boolean parameters approach" that I
suggested a while back.

 
   // Determine if the resource requires swizzling.
-  virtual bool GetResourceRequiresSwizzle() const = 0;
+  virtual bool GetResourceRequiresSwizzle(bool must_support_alpha) const = 0;
 
  protected:
   virtual ~TileTaskRunner() {}