Remove flakiness from one copy partial raster tests

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 <stddef.h>
 
 #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/display_item_list_settings.h"
 #include "cc/playback/drawing_display_item.h"
 #include "cc/test/layer_tree_pixel_test.h"
+#include "cc/test/test_compositor_frame_sink.h"
+#include "gpu/command_buffer/client/gles2_interface.h"
 #include "third_party/skia/include/core/SkCanvas.h"
 #include "third_party/skia/include/core/SkPictureRecorder.h"
 
 #if !defined(OS_ANDROID)
 
 namespace cc {
 namespace {
 
 enum RasterMode {
   PARTIAL_ONE_COPY,
@@ skipping 144 matching lines @@
         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;
     }
   }
 
+  void WillPrepareTilesOnThread(LayerTreeHostImpl* host_impl) override {
+    // Issue a GL finish before preparing tiles to ensure resources become
+    // available for use in a timely manner. Needed for the one-copy path.
+    ContextProvider* context_provider =
+        host_impl->compositor_frame_sink()->worker_context_provider();
+    if (!context_provider)
+      return;
+
+    ContextProvider::ScopedContextLock lock(context_provider);
+    lock.ContextGL()->Finish();
+  }
+
  protected:
   BlueYellowClient client_;
   scoped_refptr<PictureLayer> picture_layer_;
 };
 
 TEST_F(LayerTreeHostTilesTestPartialInvalidation,
        PartialRaster_SingleThread_OneCopy) {
   RunRasterPixelTest(
       false, PARTIAL_ONE_COPY, picture_layer_,
       base::FilePath(FILE_PATH_LITERAL("blue_yellow_partial_flipped.png")));
@@ skipping 45 matching lines @@
        FullRaster_SingleThread_GpuRaster) {
   RunRasterPixelTest(
       false, FULL_GPU, picture_layer_,
       base::FilePath(FILE_PATH_LITERAL("blue_yellow_flipped.png")));
 }
 
 }  // namespace
 }  // namespace cc
 
 #endif  // !defined(OS_ANDROID)