Update from chromium https://crrev.com/302282

cc/trees/layer_tree_host_unittest.cc

Index: cc/trees/layer_tree_host_unittest.cc
diff --git a/cc/trees/layer_tree_host_unittest.cc b/cc/trees/layer_tree_host_unittest.cc
index d15c6a328f08fdeea18765bf5dff9034167600c6..20632174987f283f13b5f775b0d26ccdde58d1f2 100644
--- a/cc/trees/layer_tree_host_unittest.cc
+++ b/cc/trees/layer_tree_host_unittest.cc
@@ -4160,6 +4160,8 @@ class LayerTreeHostTestMaxTransferBufferUsageBytes : public LayerTreeHostTest {
  protected:
   void InitializeSettings(LayerTreeSettings* settings) override {
     settings->impl_side_painting = true;
+    settings->use_zero_copy = false;
+    settings->use_one_copy = false;
   }
 
   scoped_ptr<FakeOutputSurface> CreateFakeOutputSurface(
@@ -5128,4 +5130,55 @@ class LayerTreeHostTestSynchronousCompositeSwapPromise
 // Impl-side painting is not supported for synchronous compositing.
 SINGLE_THREAD_NOIMPL_TEST_F(LayerTreeHostTestSynchronousCompositeSwapPromise);
 
+// Make sure page scale and top control deltas are applied to the client even
+// when the LayerTreeHost doesn't have a root layer.
+class LayerTreeHostAcceptsDeltasFromImplWithoutRootLayer
+    : public LayerTreeHostTest {
+ public:
+  LayerTreeHostAcceptsDeltasFromImplWithoutRootLayer()
+      : deltas_sent_to_client_(false) {}
+
+  void BeginTest() override {
+    layer_tree_host()->SetRootLayer(nullptr);
+    info_.page_scale_delta = 3.14f;
+    info_.top_controls_delta = 2.73f;
+
+    PostSetNeedsCommitToMainThread();
+  }
+
+  void BeginMainFrame(const BeginFrameArgs& args) override {
+    EXPECT_EQ(nullptr, layer_tree_host()->root_layer());
+
+    layer_tree_host()->ApplyScrollAndScale(&info_);
+    EndTest();
+  }
+
+  void ApplyViewportDeltas(
+      const gfx::Vector2d& inner,
+      const gfx::Vector2d& outer,
+      float scale_delta,
+      float top_controls_delta) override {
+    EXPECT_EQ(info_.page_scale_delta, scale_delta);
+    EXPECT_EQ(info_.top_controls_delta, top_controls_delta);
+    deltas_sent_to_client_ = true;
+  }
+
+  void ApplyViewportDeltas(
+      const gfx::Vector2d& scroll,
+      float scale_delta,
+      float top_controls_delta) override {
+    EXPECT_EQ(info_.page_scale_delta, scale_delta);
+    EXPECT_EQ(info_.top_controls_delta, top_controls_delta);
+    deltas_sent_to_client_ = true;
+  }
+
+  void AfterTest() override {
+    EXPECT_TRUE(deltas_sent_to_client_);
+  }
+
+  ScrollAndScaleSet info_;
+  bool deltas_sent_to_client_;
+};
+
+MULTI_THREAD_TEST_F(LayerTreeHostAcceptsDeltasFromImplWithoutRootLayer);
 }  // namespace cc