Enable --prefer-compositing-to-lcd-text on Chrome OS by default.

content/renderer/render_view_impl.cc

 // Copyright (c) 2012 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 "content/renderer/render_view_impl.h"
 
 #include <algorithm>
 #include <cmath>
 #include <memory>
 
@@ skipping 311 matching lines @@
       return WindowOpenDisposition::NEW_POPUP;
   default:
     NOTREACHED() << "Unexpected WebNavigationPolicy";
     return WindowOpenDisposition::IGNORE_ACTION;
   }
 }
 
 // Returns true if the device scale is high enough that losing subpixel
 // antialiasing won't have a noticeable effect on text quality.
 static bool DeviceScaleEnsuresTextQuality(float device_scale_factor) {
-#if defined(OS_ANDROID)
-  // On Android, we never have subpixel antialiasing.
+#if defined(OS_ANDROID) || defined(OS_CHROMEOS)
+  // On Android, we never have subpixel antialiasing. On Chrome OS we prefer to
+  // composite all scrollers so that we get animated overlay scrollbars.
   return true;
 #else
   // 1.5 is a common touchscreen tablet device scale factor. For such
   // devices main thread antialiasing is a heavy burden.
   return device_scale_factor >= 1.5f;
 #endif
 }
 
 static bool PreferCompositingToLCDText(CompositorDependencies* compositor_deps,
                                        float device_scale_factor) {
@@ skipping 2368 matching lines @@
                             INPUT_EVENT_ACK_STATE_NOT_CONSUMED);
   }
 
   std::unique_ptr<InputEventAck> ack(
       new InputEventAck(InputEventAckSource::MAIN_THREAD, input_event->type(),
                         INPUT_EVENT_ACK_STATE_NOT_CONSUMED));
   OnInputEventAck(std::move(ack));
 }
 
 }  // namespace content