Temporary fix for top controls ratio propagation from main to impl

The impl tree viewport changes caused by |top_controls_shown_ratio_|
changes are not reflected on the main thread when the top controls are
partially shown. This causes a mismatch each time we push property trees
from main > impl.

This change provides a temporary fix by updating the viewport any time
we push main > impl when in a partially shown state.

Long term we should propagate these changes to the main tree and
avoid this workaround.

Bug: 875943
Change-Id: I47e6a5127e6a2c76b5286e257904d2501e3859a2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1795572
Commit-Queue: Eric Karl <ericrk@chromium.org>
Commit-Queue: Khushal <khushalsagar@chromium.org>
Reviewed-by: Khushal <khushalsagar@chromium.org>
Auto-Submit: Eric Karl <ericrk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#695372}

cc/trees/layer_tree_host.cc

@@ -1619,6 +1619,15 @@ void LayerTreeHost::PushLayerTreePropertiesTo(LayerTreeImpl* tree_impl) {
     tree_impl->RequestForceSendMetadata();
 
   tree_impl->set_has_ever_been_drawn(false);
+
+  // TODO(ericrk): The viewport changes caused by |top_controls_shown_ratio_|
+  // changes should propagate back to the main tree. This does not currently
+  // happen, so we must force the impl tree to update its viewports if
+  // |top_controls_shown_ratio_| is greater than 0.0f and less than 1.0f
+  // (partially shown). crbug.com/875943
+  if (top_controls_shown_ratio_ > 0.0f && top_controls_shown_ratio_ < 1.0f) {
+    tree_impl->UpdateViewportContainerSizes();
+  }
 }
 
 void LayerTreeHost::PushSurfaceRangesTo(LayerTreeImpl* tree_impl) {

cc/trees/layer_tree_host_unittest.cc

@@ -8811,5 +8811,52 @@ class LayerTreeHostTestPartialTileDamage : public LayerTreeHostTest {
 
 MULTI_THREAD_TEST_F(LayerTreeHostTestPartialTileDamage);
 
+// Make sure that a change in top controls shown ratio causes an update to the
+// pending tree's viewports.
+class LayerTreeHostTopControlsDeltaTriggersViewportUpdate
+    : public LayerTreeHostTest {
+ public:
+  void BeginTest() override { PostSetNeedsCommitToMainThread(); }
+
+  void SetupTree() override {
+    LayerTreeHostTest::SetupTree();
+    Layer* root_layer = layer_tree_host()->root_layer();
+    // Set up scrollable root.
+    root_layer->SetBounds(gfx::Size(100, 100));
+    SetupViewport(root_layer, gfx::Size(50, 50), root_layer->bounds());
+    // Set browser controls to be partially shown.
+    layer_tree_host()->SetBrowserControlsHeight(kTopControlsHeight, 0.0f,
+                                                true /* shrink */);
+    layer_tree_host()->SetBrowserControlsShownRatio(kTopControlsShownRatio);
+  }
+
+  void BeginCommitOnThread(LayerTreeHostImpl* impl) override {
+    // Before commit the inner_viewport_container_bounds_delta() value should
+    // not reflect the partially shown top controls.
+    float bounds_delta = impl->pending_tree()
+                             ->property_trees()
+                             ->inner_viewport_container_bounds_delta()
+                             .y();
+    EXPECT_EQ(bounds_delta, 0.0f);
+  }
+
+  void CommitCompleteOnThread(LayerTreeHostImpl* impl) override {
+    // After commit the inner_viewport_container_bounds_delta() value should
+    // reflect the partially shown top controls.
+    float bounds_delta = impl->pending_tree()
+                             ->property_trees()
+                             ->inner_viewport_container_bounds_delta()
+                             .y();
+    EXPECT_EQ(bounds_delta,
+              kTopControlsHeight - kTopControlsHeight * kTopControlsShownRatio);
+    EndTest();
+  }
+
+  static constexpr float kTopControlsHeight = 10.0f;
+  static constexpr float kTopControlsShownRatio = 0.3f;
+};
+
+MULTI_THREAD_TEST_F(LayerTreeHostTopControlsDeltaTriggersViewportUpdate);
+
 }  // namespace
 }  // namespace cc