Plumb an overscroll callback form the compositor to the Android UI thread.

cc/layer_tree_host_impl_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/layer_tree_host_impl.h"
 
 #include <cmath>
 
 #include "base/bind.h"
 #include "base/command_line.h"
@@ skipping 893 matching lines @@
         EXPECT_EQ(0.5f, metadata.min_page_scale_factor);
         EXPECT_EQ(4.0f, metadata.max_page_scale_factor);
     }
 
     // Scrolling should update metadata immediately.
     EXPECT_EQ(m_hostImpl->scrollBegin(gfx::Point(0, 0), InputHandlerClient::Wheel), InputHandlerClient::ScrollStarted);
     m_hostImpl->scrollBy(gfx::Point(), gfx::Vector2d(0, 10));
     {
         CompositorFrameMetadata metadata = m_hostImpl->makeCompositorFrameMetadata();
         EXPECT_EQ(gfx::Vector2dF(0.0f, 10.0f), metadata.root_scroll_offset);
+        EXPECT_EQ(gfx::Vector2dF(0.0f, 0.0f), metadata.unused_scroll_delta);
     }
+    // Overscroll should update metadata immediately.
+    m_hostImpl->scrollBy(gfx::Point(), gfx::Vector2d(0, 50));
+    {
+        CompositorFrameMetadata metadata = m_hostImpl->makeCompositorFrameMetadata();
+        EXPECT_EQ(gfx::Vector2dF(0.0f, 50.0f), metadata.root_scroll_offset);
+        EXPECT_EQ(gfx::Vector2dF(0.0f, 10.0f), metadata.unused_scroll_delta);
+    }
+    m_hostImpl->scrollBy(gfx::Point(), gfx::Vector2d(0, -40));
     m_hostImpl->scrollEnd();
 
     {
         CompositorFrameMetadata metadata = m_hostImpl->makeCompositorFrameMetadata();
         EXPECT_EQ(gfx::Vector2dF(0.0f, 10.0f), metadata.root_scroll_offset);
     }
 
     // Page scale should update metadata correctly (shrinking only the viewport).
     m_hostImpl->pinchGestureBegin();
     m_hostImpl->pinchGestureUpdate(2.0f, gfx::Point(0, 0));
@@ skipping 3751 matching lines @@
         m_hostImpl->didDrawAllLayers(frame);
     }
 }
 
 INSTANTIATE_TEST_CASE_P(LayerTreeHostImplTests,
                         LayerTreeHostImplTest,
                         ::testing::Values(false, true));
 
 }  // namespace
 }  // namespace cc