Don't set sent_top_controls_delta when root layer doesn't exist.

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 79abc1c02f2ef28116296a3c79f43ce0a1a998c2..a70382db095ac9668ef191713c8e7b634405c6d6 100644
--- a/cc/trees/layer_tree_host_impl_unittest.cc
+++ b/cc/trees/layer_tree_host_impl_unittest.cc
@@ -2250,8 +2250,6 @@ class LayerTreeHostImplTopControlsTest : public LayerTreeHostImplTest {
   }
 
   void SetupTopControlsAndScrollLayer() {
-    CreateHostImpl(settings_, CreateOutputSurface());
-
     scoped_ptr<LayerImpl> root =
         LayerImpl::Create(host_impl_->active_tree(), 1);
     scoped_ptr<LayerImpl> root_clip =
@@ -2274,8 +2272,6 @@ class LayerTreeHostImplTopControlsTest : public LayerTreeHostImplTest {
     host_impl_->SetViewportSize(viewport_size_);
     host_impl_->SetTopControlsLayoutHeight(
         settings_.top_controls_height);
-    LayerImpl* root_clip_ptr = host_impl_->active_tree()->root_layer();
-    EXPECT_EQ(clip_size_, root_clip_ptr->bounds());
 
     host_impl_->CreatePendingTree();
     root =
@@ -2300,8 +2296,6 @@ class LayerTreeHostImplTopControlsTest : public LayerTreeHostImplTest {
     host_impl_->SetViewportSize(viewport_size_);
     host_impl_->sync_tree()->set_top_controls_layout_height(
         settings_.top_controls_height);
-    root_clip_ptr = host_impl_->sync_tree()->root_layer();
-    EXPECT_EQ(clip_size_, root_clip_ptr->bounds());
   }
 
  protected:
@@ -2312,7 +2306,30 @@ class LayerTreeHostImplTopControlsTest : public LayerTreeHostImplTest {
   LayerTreeSettings settings_;
 };  // class LayerTreeHostImplTopControlsTest
 
+TEST_F(LayerTreeHostImplTopControlsTest,
+       TopControlsDeltaOnlySentWithRootLayer) {
+  CreateHostImpl(settings_, CreateOutputSurface());
+
+  host_impl_->active_tree()->set_top_controls_delta(-20.f);
+
+  // Because LTH::ApplyScrollAndScale doesn't know what to do with a scroll
+  // delta packet when the root layer doesn't exist yet, make sure not to set
+  // sent_top_controls_delta either to avoid the delta getting clobbered on the
+  // next commit.
+  scoped_ptr<ScrollAndScaleSet> scroll_info = host_impl_->ProcessScrollDeltas();
+  EXPECT_EQ(scroll_info->top_controls_delta, 0.f);
+  EXPECT_EQ(host_impl_->active_tree()->sent_top_controls_delta(), 0.f);
+
+  SetupTopControlsAndScrollLayer();
+
+  // After the root layer exists, it should be set normally.
+  scroll_info = host_impl_->ProcessScrollDeltas();
+  EXPECT_EQ(scroll_info->top_controls_delta, -20.f);
+  EXPECT_EQ(host_impl_->active_tree()->sent_top_controls_delta(), -20.f);
+}
+
 TEST_F(LayerTreeHostImplTopControlsTest, ScrollTopControlsByFractionalAmount) {
+  CreateHostImpl(settings_, CreateOutputSurface());
   SetupTopControlsAndScrollLayer();
   DrawFrame();
 
@@ -2336,6 +2353,7 @@ TEST_F(LayerTreeHostImplTopControlsTest, ScrollTopControlsByFractionalAmount) {
 }
 
 TEST_F(LayerTreeHostImplTopControlsTest, ScrollTopControlsWithPageScale) {
+  CreateHostImpl(settings_, CreateOutputSurface());
   SetupTopControlsAndScrollLayer();
   DrawFrame();
 
@@ -2369,6 +2387,7 @@ TEST_F(LayerTreeHostImplTopControlsTest, ScrollTopControlsWithPageScale) {
 // Ensure setting the top controls position explicitly using the setters on the
 // TreeImpl correctly affects the top controls manager and viewport bounds.
 TEST_F(LayerTreeHostImplTopControlsTest, PositionTopControlsExplicitly) {
+  CreateHostImpl(settings_, CreateOutputSurface());
   SetupTopControlsAndScrollLayer();
   DrawFrame();
 
@@ -2392,6 +2411,7 @@ TEST_F(LayerTreeHostImplTopControlsTest, PositionTopControlsExplicitly) {
 // applied on sync tree activation. The total top controls offset shouldn't
 // change after the activation.
 TEST_F(LayerTreeHostImplTopControlsTest, ApplyDeltaOnTreeActivation) {
+  CreateHostImpl(settings_, CreateOutputSurface());
   SetupTopControlsAndScrollLayer();
   DrawFrame();
 
@@ -2426,6 +2446,7 @@ TEST_F(LayerTreeHostImplTopControlsTest, ApplyDeltaOnTreeActivation) {
 // height is the amount that the inner viewport container was shrunk outside
 // the compositor to accommodate the top controls.
 TEST_F(LayerTreeHostImplTopControlsTest, TopControlsLayoutHeightChanged) {
+  CreateHostImpl(settings_, CreateOutputSurface());
   SetupTopControlsAndScrollLayer();
   DrawFrame();
 
@@ -2467,6 +2488,7 @@ TEST_F(LayerTreeHostImplTopControlsTest, TopControlsLayoutHeightChanged) {
 
 TEST_F(LayerTreeHostImplTopControlsTest,
        ScrollNonScrollableRootWithTopControls) {
+  CreateHostImpl(settings_, CreateOutputSurface());
   SetupTopControlsAndScrollLayer();
   DrawFrame();