Route Scroll events through a cc::InputHandler

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 2939 matching lines @@
   bool is_viewport_scroll_layer =
       viewport()->MainScrollLayer() &&
       scroll_node->owner_id == viewport()->MainScrollLayer()->id();
 
   // This is needed if the scroll chains up to the viewport without going
   // through the outer viewport scroll layer. This can happen if we scroll an
   // element that's not a descendant of the document.rootScroller. In that case
   // we want to scroll the inner viewport -- to allow panning while zoomed --
   // but also move browser controls if needed.
   bool is_inner_viewport_scroll_layer =
+      InnerViewportScrollLayer() &&
       scroll_node->owner_id == InnerViewportScrollLayer()->id();
 
   if (is_viewport_scroll_layer || is_inner_viewport_scroll_layer) {
     Viewport::ScrollResult result = viewport()->ScrollBy(
         delta, viewport_point, scroll_state->is_direct_manipulation(),
         !wheel_scrolling_, is_viewport_scroll_layer);
 
     applied_delta = result.consumed_delta;
     delta_applied_to_content = result.content_scrolled_delta;
   } else {
@@ skipping 74 matching lines @@
   scroll_state->set_scroll_chain_and_layer_tree(current_scroll_chain,
                                                 active_tree());
   scroll_state->DistributeToScrollChainDescendant();
 }
 
 InputHandlerScrollResult LayerTreeHostImpl::ScrollBy(
     ScrollState* scroll_state) {
   DCHECK(scroll_state);
 
   TRACE_EVENT0("cc", "LayerTreeHostImpl::ScrollBy");
+
+  if (!CurrentlyScrollingLayer()) {
+    // If the InputHandlerClient didn't call ScrollBegin() to re-perform a
+    // hit-test but provided an element to scroll instead, scroll that.
+    ElementId provided_element =
+        scroll_state->data()->current_native_scrolling_element();
+    if (provided_element) {
+      // Assume the primaryId matches the layer_id for lookup (this is true for
+      // ui:Layers), then check the match.
+      LayerImpl* layer = active_tree()->LayerById(provided_element.primaryId);
+      if (layer && layer->element_id() == provided_element)
+        active_tree_->SetCurrentlyScrollingLayer(layer);
+    }
+  }
+
   if (!CurrentlyScrollingLayer())
     return InputHandlerScrollResult();
 
   float initial_top_controls_offset =
       browser_controls_offset_manager_->ControlsTopOffset();
 
   scroll_state->set_delta_consumed_for_scroll_sequence(
       did_lock_scrolling_layer_);
   scroll_state->set_is_direct_manipulation(!wheel_scrolling_);
   scroll_state->set_current_native_scrolling_node(
@@ skipping 993 matching lines @@
       worker_context_visibility_ =
           worker_context->CacheController()->ClientBecameVisible();
     } else {
       worker_context->CacheController()->ClientBecameNotVisible(
           std::move(worker_context_visibility_));
     }
   }
 }
 
 }  // namespace cc