Revert of Fix scroll chaining for non-descendants of root scroller.

cc/trees/layer_tree_host_impl.cc

 // Copyright 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/trees/layer_tree_host_impl.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 2549 matching lines @@
       }
 
       if (status.thread == InputHandler::SCROLL_ON_IMPL_THREAD &&
           !potentially_scrolling_layer_impl) {
         potentially_scrolling_layer_impl =
             active_tree_->LayerById(scroll_node->owner_id);
       }
     }
   }
 
-  // The outer viewport layer represents the viewport.
-  if (potentially_scrolling_layer_impl == InnerViewportScrollLayer())
-    potentially_scrolling_layer_impl = OuterViewportScrollLayer();
+  // Falling back to the root scroll layer ensures generation of root overscroll
+  // notifications. The inner viewport layer represents the viewport during
+  // scrolling.
+  if (!potentially_scrolling_layer_impl)
+    potentially_scrolling_layer_impl = InnerViewportScrollLayer();
 
-  // Falling back to the root scroll layer ensures generation of root overscroll
-  // notifications.
-  if (!potentially_scrolling_layer_impl)
-    potentially_scrolling_layer_impl = OuterViewportScrollLayer();
+  // The inner viewport layer represents the viewport.
+  if (potentially_scrolling_layer_impl == OuterViewportScrollLayer())
+    potentially_scrolling_layer_impl = InnerViewportScrollLayer();
 
   if (potentially_scrolling_layer_impl) {
     // Ensure that final layer scrolls on impl thread (crbug.com/625100)
     ScrollNode* scroll_node =
         scroll_tree.Node(potentially_scrolling_layer_impl->scroll_tree_index());
     ScrollStatus status =
         TryScroll(device_viewport_point, type, scroll_tree, scroll_node);
     if (IsMainThreadScrolling(status, scroll_node)) {
       *scroll_on_main_thread = true;
       *main_thread_scrolling_reasons = status.main_thread_scrolling_reasons;
@@ skipping 252 matching lines @@
   // that can scroll and set up an animation of its scroll offset. Note that
   // this does not currently go through the scroll customization machinery
   // that ScrollBy uses for non-animated wheel scrolls.
   scroll_status = ScrollBegin(&scroll_state, WHEEL);
   scroll_node = scroll_tree.CurrentlyScrollingNode();
   if (scroll_status.thread == SCROLL_ON_IMPL_THREAD) {
     gfx::Vector2dF pending_delta = scroll_delta;
     if (scroll_node) {
       for (; scroll_tree.parent(scroll_node);
            scroll_node = scroll_tree.parent(scroll_node)) {
-        if (!scroll_node->scrollable)
+        if (!scroll_node->scrollable ||
+            scroll_node->is_outer_viewport_scroll_layer)
           continue;
 
-        if (scroll_node->is_outer_viewport_scroll_layer ||
-            scroll_node->is_inner_viewport_scroll_layer) {
+        if (scroll_node->is_inner_viewport_scroll_layer) {
           gfx::Vector2dF scrolled =
               viewport()->ScrollAnimated(pending_delta, delayed_by);
           // Viewport::ScrollAnimated returns pending_delta as long as it
           // starts an animation.
           if (scrolled == pending_delta)
             return scroll_status;
-          break;
+          pending_delta -= scrolled;
+          continue;
         }
 
         gfx::Vector2dF scroll_delta =
             ComputeScrollDelta(scroll_node, pending_delta);
         if (ScrollAnimationCreate(scroll_node, scroll_delta, delayed_by))
           return scroll_status;
 
         pending_delta -= scroll_delta;
       }
     }
@@ skipping 122 matching lines @@
                                     ScrollState* scroll_state) {
   DCHECK(scroll_state);
   gfx::Point viewport_point(scroll_state->position_x(),
                             scroll_state->position_y());
   const gfx::Vector2dF delta(scroll_state->delta_x(), scroll_state->delta_y());
   gfx::Vector2dF applied_delta;
   // TODO(tdresser): Use a more rational epsilon. See crbug.com/510550 for
   // details.
   const float kEpsilon = 0.1f;
 
-  if (scroll_node->is_outer_viewport_scroll_layer) {
+  if (scroll_node->is_inner_viewport_scroll_layer) {
     bool affect_top_controls = !wheel_scrolling_;
     Viewport::ScrollResult result = viewport()->ScrollBy(
         delta, viewport_point, scroll_state->is_direct_manipulation(),
         affect_top_controls);
     applied_delta = result.consumed_delta;
     scroll_state->set_caused_scroll(
         std::abs(result.content_scrolled_delta.x()) > kEpsilon,
         std::abs(result.content_scrolled_delta.y()) > kEpsilon);
     scroll_state->ConsumeDelta(applied_delta.x(), applied_delta.y());
   } else {
     applied_delta = ScrollSingleNode(
         scroll_node, delta, viewport_point,
         scroll_state->is_direct_manipulation(),
         &scroll_state->layer_tree_impl()->property_trees()->scroll_tree);
   }
 
   // If the layer wasn't able to move, try the next one in the hierarchy.
   bool scrolled = std::abs(applied_delta.x()) > kEpsilon;
   scrolled = scrolled || std::abs(applied_delta.y()) > kEpsilon;
 
-  if (scrolled && !scroll_node->is_outer_viewport_scroll_layer) {
+  if (scrolled && !scroll_node->is_inner_viewport_scroll_layer) {
     // If the applied delta is within 45 degrees of the input
     // delta, bail out to make it easier to scroll just one layer
     // in one direction without affecting any of its parents.
     float angle_threshold = 45;
     if (MathUtil::SmallestAngleBetweenVectors(applied_delta, delta) <
         angle_threshold) {
       applied_delta = delta;
     } else {
       // Allow further movement only on an axis perpendicular to the direction
       // in which the layer moved.
@@ skipping 16 matching lines @@
   // sides but it may become a non issue if we get rid of scroll chaining (see
   // crbug.com/526462)
   std::list<const ScrollNode*> current_scroll_chain;
   ScrollTree& scroll_tree = active_tree_->property_trees()->scroll_tree;
   ScrollNode* scroll_node = scroll_tree.CurrentlyScrollingNode();
   if (scroll_node) {
     for (; scroll_tree.parent(scroll_node);
          scroll_node = scroll_tree.parent(scroll_node)) {
       if (scroll_node->is_outer_viewport_scroll_layer) {
         // Don't chain scrolls past the outer viewport scroll layer. Once we
-        // reach that, we're viewport scrolling which is special and handled by
-        // cc's Viewport class.
-        current_scroll_chain.push_front(scroll_node);
+        // reach that, we should scroll the viewport, which is represented by
+        // the inner viewport scroll layer.
+        ScrollNode* inner_viewport_scroll_node =
+            scroll_tree.Node(InnerViewportScrollLayer()->scroll_tree_index());
+        current_scroll_chain.push_front(inner_viewport_scroll_node);
         break;
       }
 
       if (!scroll_node->scrollable)
         continue;
 
       current_scroll_chain.push_front(scroll_node);
     }
   }
   scroll_state->set_scroll_chain_and_layer_tree(current_scroll_chain,
@@ skipping 153 matching lines @@
       active_tree_->FindLayerThatIsHitByPoint(device_viewport_point);
   HandleMouseOverScrollbar(layer_impl);
   if (scroll_layer_id_when_mouse_over_scrollbar_ != Layer::INVALID_ID)
     return;
 
   bool scroll_on_main_thread = false;
   uint32_t main_thread_scrolling_reasons;
   LayerImpl* scroll_layer_impl = FindScrollLayerForDeviceViewportPoint(
       device_viewport_point, InputHandler::TOUCHSCREEN, layer_impl,
       &scroll_on_main_thread, &main_thread_scrolling_reasons);
+  if (scroll_layer_impl == InnerViewportScrollLayer())
+    scroll_layer_impl = OuterViewportScrollLayer();
   if (scroll_on_main_thread || !scroll_layer_impl)
     return;
 
   ScrollbarAnimationController* animation_controller =
       ScrollbarAnimationControllerForId(scroll_layer_impl->id());
   if (!animation_controller)
     return;
 
   float distance_to_scrollbar = std::numeric_limits<float>::max();
   for (ScrollbarLayerImplBase* scrollbar :
@@ skipping 27 matching lines @@
           scroll_layer_id_when_mouse_over_scrollbar_);
   if (new_animation_controller)
     new_animation_controller->DidMouseMoveNear(0);
 }
 
 void LayerTreeHostImpl::PinchGestureBegin() {
   pinch_gesture_active_ = true;
   client_->RenewTreePriority();
   pinch_gesture_end_should_clear_scrolling_layer_ = !CurrentlyScrollingLayer();
   active_tree_->SetCurrentlyScrollingLayer(
-      active_tree_->OuterViewportScrollLayer());
+      active_tree_->InnerViewportScrollLayer());
   top_controls_manager_->PinchBegin();
 }
 
 void LayerTreeHostImpl::PinchGestureUpdate(float magnify_delta,
                                            const gfx::Point& anchor) {
   TRACE_EVENT0("cc", "LayerTreeHostImpl::PinchGestureUpdate");
   if (!InnerViewportScrollLayer())
     return;
   viewport()->PinchUpdate(magnify_delta, anchor);
   client_->SetNeedsCommitOnImplThread();
@@ skipping 851 matching lines @@
   if (is_visible) {
     worker_context_visibility_ =
         worker_context->CacheController()->ClientBecameVisible();
   } else {
     worker_context->CacheController()->ClientBecameNotVisible(
         std::move(worker_context_visibility_));
   }
 }
 
 }  // namespace cc