Remove image_decode_tasks_enabled flag.

cc/trees/layer_tree_host_unittest.cc

 // Copyright 2011 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/trees/layer_tree_host.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 7161 matching lines @@
 
   void SetupTree() override {
     client_.set_fill_with_nonsolid_color(true);
 
     std::unique_ptr<FakeRecordingSource> recording =
         FakeRecordingSource::CreateFilledRecordingSource(
             gfx::Size(10000, 10000));
 
     recording->add_draw_image(CreateDiscardableImage(large_image_size_),
                               gfx::Point(0, 0));
-    recording->SetGenerateDiscardableImagesMetadata(true);
     recording->Rerecord();
 
     scoped_refptr<FakePictureLayer> root =
         FakePictureLayer::CreateWithRecordingSource(&client_,
                                                     std::move(recording));
     root->SetBounds(gfx::Size(10000, 10000));
     client_.set_bounds(root->bounds());
     root->SetContentsOpaque(true);
 
     layer_tree_host()->SetRootLayer(root);
@@ skipping 402 matching lines @@
   void AfterTest() override {}
 
  private:
   bool received_ack_ = false;
 };
 
 SINGLE_AND_MULTI_THREAD_TEST_F(LayerTreeHostTestDiscardAckAfterRelease);
 
 }  // namespace
 }  // namespace cc