Use regular bubbling scroll for scrolling during pinch gesture.

Scrolls occuring during a pinch gesture, that is, moving the center of pinch
during the gesture, are treated as regular scrolls that bubble from one viewport
layer to the next.

Note, scrolls during a pinch made in order to keep the pinch point centered
remain unchanged: under the --invert-viewport-scroll-order flag, these scrolls
will "pan" the viewport, scrolling *only* the inner viewport.

BUG=433724
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel

Review URL: https://codereview.chromium.org/1288773002

Cr-Commit-Position: refs/heads/master@{#343112}

2 files changed, 28 insertions, 11 deletions

diff --git a/cc/trees/layer_tree_host_impl.cc b/cc/trees/layer_tree_host_impl.cc
index 0d44c41..1ebc60f 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -2696,13 +2696,6 @@ InputHandlerScrollResult LayerTreeHostImpl::ScrollBy(
   if (!CurrentlyScrollingLayer())
     return InputHandlerScrollResult();
 
-  if (pinch_gesture_active_ && settings().invert_viewport_scroll_order) {
-    // Scrolls during a pinch gesture should pan the visual viewport, rather
-    // than a typical bubbling scroll.
-    viewport()->Pan(scroll_delta);
-    return InputHandlerScrollResult();
-  }
-
   float initial_top_controls_offset =
       top_controls_manager_->ControlsTopOffset();
   ScrollState scroll_state(
diff --git a/cc/trees/layer_tree_host_impl_unittest.cc b/cc/trees/layer_tree_host_impl_unittest.cc
index b8dbc1e..55b2607 100644
--- a/cc/trees/layer_tree_host_impl_unittest.cc
+++ b/cc/trees/layer_tree_host_impl_unittest.cc
@@ -1193,7 +1193,10 @@ TEST_F(LayerTreeHostImplTest, ViewportScrollOrder) {
       outer_scroll_layer->CurrentScrollOffset());
 }
 
-TEST_F(LayerTreeHostImplTest, ScrollDuringPinchScrollsInnerViewport) {
+// Tests that scrolls during a pinch gesture (i.e. "two-finger" scrolls) work
+// as expected. That is, scrolling during a pinch should bubble from the inner
+// to the outer viewport.
+TEST_F(LayerTreeHostImplTest, ScrollDuringPinchGesture) {
   LayerTreeSettings settings = DefaultSettings();
   settings.invert_viewport_scroll_order = true;
   CreateHostImpl(settings,
@@ -1213,17 +1216,38 @@ TEST_F(LayerTreeHostImplTest, ScrollDuringPinchScrollsInnerViewport) {
 
   host_impl_->ScrollBegin(gfx::Point(250, 250), InputHandler::GESTURE);
   host_impl_->PinchGestureBegin();
+
   host_impl_->PinchGestureUpdate(2, gfx::Point(250, 250));
-  host_impl_->ScrollBy(gfx::Point(250, 250), gfx::Vector2dF(10.f, 10.f));
-  host_impl_->PinchGestureEnd();
-  host_impl_->ScrollEnd();
+  EXPECT_VECTOR_EQ(
+      gfx::Vector2dF(0, 0),
+      outer_scroll_layer->CurrentScrollOffset());
+  EXPECT_VECTOR_EQ(
+      gfx::Vector2dF(125, 125),
+      inner_scroll_layer->CurrentScrollOffset());
 
+  // Needed so that the pinch is accounted for in draw properties.
+  DrawFrame();
+
+  host_impl_->ScrollBy(gfx::Point(250, 250), gfx::Vector2dF(10.f, 10.f));
   EXPECT_VECTOR_EQ(
       gfx::Vector2dF(0, 0),
       outer_scroll_layer->CurrentScrollOffset());
   EXPECT_VECTOR_EQ(
       gfx::Vector2dF(130, 130),
       inner_scroll_layer->CurrentScrollOffset());
+
+  DrawFrame();
+
+  host_impl_->ScrollBy(gfx::Point(250, 250), gfx::Vector2dF(400.f, 400.f));
+  EXPECT_VECTOR_EQ(
+      gfx::Vector2dF(80, 80),
+      outer_scroll_layer->CurrentScrollOffset());
+  EXPECT_VECTOR_EQ(
+      gfx::Vector2dF(250, 250),
+      inner_scroll_layer->CurrentScrollOffset());
+
+  host_impl_->PinchGestureEnd();
+  host_impl_->ScrollEnd();
 }
 
 // Tests the "snapping" of pinch-zoom gestures to the screen edge. That is, when