Defer scroll status determination until scrolling has occurred

cc/trees/layer_tree_host_impl_unittest.cc

Index: cc/trees/layer_tree_host_impl_unittest.cc
diff --git a/cc/trees/layer_tree_host_impl_unittest.cc b/cc/trees/layer_tree_host_impl_unittest.cc
index 5e51cc37aeefa0f36d6c8e8dd5c1703fb15cb52e..684e1099ccdc35a4e460c0564187cb7b74ad9ec1 100644
--- a/cc/trees/layer_tree_host_impl_unittest.cc
+++ b/cc/trees/layer_tree_host_impl_unittest.cc
@@ -512,6 +512,20 @@ TEST_F(LayerTreeHostImplTest, ScrollRootCallsCommitAndRedraw) {
   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,