Keep expanded if mouse moves off of scrollbar while dragging

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 191 matching lines @@
       content_is_suitable_for_gpu_rasterization_(true),
       has_gpu_rasterization_trigger_(false),
       use_gpu_rasterization_(false),
       use_msaa_(false),
       gpu_rasterization_status_(GpuRasterizationStatus::OFF_DEVICE),
       input_handler_client_(NULL),
       did_lock_scrolling_layer_(false),
       wheel_scrolling_(false),
       scroll_affects_scroll_handler_(false),
       scroll_layer_id_when_mouse_over_scrollbar_(Layer::INVALID_ID),
+      captured_scrollbar_layer_id_(Layer::INVALID_ID),
       tile_priorities_dirty_(false),
       settings_(settings),
       visible_(false),
       cached_managed_memory_policy_(settings.gpu_memory_policy),
       is_synchronous_single_threaded_(!task_runner_provider->HasImplThread() &&
                                       !settings.single_thread_proxy_scheduler),
       // Must be initialized after is_synchronous_single_threaded_ and
       // task_runner_provider_.
       tile_manager_(this,
                     GetTaskRunner(),
@@ skipping 2999 matching lines @@
 
   gfx::Rect layer_impl_bounds(layer_impl->bounds());
 
   gfx::RectF device_viewport_layer_impl_bounds = MathUtil::MapClippedRect(
       layer_impl->ScreenSpaceTransform(), gfx::RectF(layer_impl_bounds));
 
   return device_viewport_layer_impl_bounds.ManhattanDistanceToPoint(
       device_viewport_point);
 }
 
+void LayerTreeHostImpl::MouseDown() {
+  if (scroll_layer_id_when_mouse_over_scrollbar_ == Layer::INVALID_ID)
+    return;
+
+  captured_scrollbar_layer_id_ = scroll_layer_id_when_mouse_over_scrollbar_;
+  ScrollbarAnimationController* animation_controller =
+      ScrollbarAnimationControllerForId(captured_scrollbar_layer_id_);
+  if (animation_controller)
+    animation_controller->DidCaptureScrollbarBegin();
+}
+
+void LayerTreeHostImpl::MouseUp() {
+  if (captured_scrollbar_layer_id_ == Layer::INVALID_ID)
+    return;
+
+  ScrollbarAnimationController* animation_controller =
+      ScrollbarAnimationControllerForId(captured_scrollbar_layer_id_);
+  if (animation_controller)
+    animation_controller->DidCaptureScrollbarEnd();
+  captured_scrollbar_layer_id_ = Layer::INVALID_ID;
+}
+
 void LayerTreeHostImpl::MouseMoveAt(const gfx::Point& viewport_point) {
   gfx::PointF device_viewport_point = gfx::ScalePoint(
       gfx::PointF(viewport_point), active_tree_->device_scale_factor());
   LayerImpl* layer_impl =
       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;
@@ skipping 919 matching lines @@
   if (is_visible) {
     worker_context_visibility_ =
         worker_context->CacheController()->ClientBecameVisible();
   } else {
     worker_context->CacheController()->ClientBecameNotVisible(
         std::move(worker_context_visibility_));
   }
 }
 
 }  // namespace cc