Re-land: cc: Use worker context for one-copy tile initialization.

cc/trees/layer_tree_host_pixeltest_tiles.cc

 // Copyright 2015 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/layers/content_layer_client.h"
 #include "cc/layers/picture_layer.h"
 #include "cc/output/copy_output_request.h"
 #include "cc/playback/display_item_list.h"
 #include "cc/playback/drawing_display_item.h"
 #include "cc/test/layer_tree_pixel_test.h"
@@ skipping 143 matching lines @@
 
   void DidCommitAndDrawFrame() override {
     switch (layer_tree_host()->source_frame_number()) {
       case 1:
         // We have done one frame, so the layer's content has been rastered.
         // Now we change the picture behind it to record something completely
         // different, but we give a smaller invalidation rect. The layer should
         // only re-raster the stuff in the rect. If it doesn't do partial raster
         // it would re-raster the whole thing instead.
         client_.set_blue_top(false);
+        Finish();
         picture_layer_->SetNeedsDisplayRect(gfx::Rect(50, 50, 100, 100));
 
         // Add a copy request to see what happened!
         DoReadback();
         break;
     }
   }
 
  protected:
   BlueYellowClient client_;
@@ skipping 39 matching lines @@
        PartialRaster_SingleThread_GpuRaster) {
   RunRasterPixelTest(
       false, GPU, picture_layer_,
       base::FilePath(FILE_PATH_LITERAL("blue_yellow_partial_flipped.png")));
 }
 
 }  // namespace
 }  // namespace cc
 
 #endif  // !defined(OS_ANDROID)