Defer scroll status determination until scrolling has occurred

cc/trees/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/trees/layer_tree_host_impl.h"
 
 #include <cmath>
 
 #include "base/bind.h"
 #include "base/command_line.h"
@@ skipping 494 matching lines @@
   host_impl_->ScrollBy(gfx::Point(), gfx::Vector2d(0, 10));
   EXPECT_TRUE(host_impl_->IsCurrentlyScrollingLayerAt(gfx::Point(0, 10),
                                                       InputHandler::Wheel));
   host_impl_->ScrollEnd();
   EXPECT_FALSE(host_impl_->IsCurrentlyScrollingLayerAt(gfx::Point(),
                                                        InputHandler::Wheel));
   EXPECT_TRUE(did_request_redraw_);
   EXPECT_TRUE(did_request_commit_);
 }
 
+TEST_F(LayerTreeHostImplTest, ScrollActiveOnlyAfterScrollMovement) {
+  SetupScrollAndContentsLayers(gfx::Size(100, 100));
+  host_impl_->SetViewportSize(gfx::Size(50, 50));
+  DrawFrame();
+
+  EXPECT_EQ(InputHandler::ScrollStarted,
+            host_impl_->ScrollBegin(gfx::Point(), InputHandler::Wheel));
+  EXPECT_FALSE(host_impl_->IsActivelyScrolling());

[brianderson, 2014/10/23 22:39:42]

Is this the expectation that would fail without your patch? If so, lgtm.

[jdduke (slow), 2014/10/23 22:45:13]

Yup, exactly.

+  host_impl_->ScrollBy(gfx::Point(), gfx::Vector2d(0, 10));
+  EXPECT_TRUE(host_impl_->IsActivelyScrolling());
+  host_impl_->ScrollEnd();
+  EXPECT_FALSE(host_impl_->IsActivelyScrolling());
+}
+
 TEST_F(LayerTreeHostImplTest, ScrollWithoutRootLayer) {
   // We should not crash when trying to scroll an empty layer tree.
   EXPECT_EQ(InputHandler::ScrollIgnored,
             host_impl_->ScrollBegin(gfx::Point(), InputHandler::Wheel));
 }
 
 TEST_F(LayerTreeHostImplTest, ScrollWithoutRenderer) {
   scoped_ptr<TestWebGraphicsContext3D> context_owned =
       TestWebGraphicsContext3D::Create();
   context_owned->set_context_lost(true);
@@ skipping 7013 matching lines @@
   // surface.
   EXPECT_EQ(0, num_lost_surfaces_);
   host_impl_->DidLoseOutputSurface();
   EXPECT_EQ(1, num_lost_surfaces_);
   host_impl_->DidLoseOutputSurface();
   EXPECT_LE(1, num_lost_surfaces_);
 }
 
 }  // namespace
 }  // namespace cc