Revert of Remove enable/disable wheel gestures setting.

cc/trees/layer_tree_host_impl_unittest.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 <algorithm>
 #include <cmath>
@@ skipping 747 matching lines @@
       host_impl_->ProcessScrollDeltas();
   EXPECT_TRUE(
       ScrollInfoContains(*scroll_info, scroll_layer->id(), scroll_delta));
 }
 
 TEST_F(LayerTreeHostImplTest, ScrollBlocksOnWheelEventHandlers) {
   SetupScrollAndContentsLayers(gfx::Size(100, 100));
   host_impl_->SetViewportSize(gfx::Size(50, 50));
   DrawFrame();
 
-  // Wheel handlers determine whether mouse events block scroll.
+  // With registered event handlers, wheel scrolls don't necessarily
+  // have to go to the main thread.
   host_impl_->active_tree()->set_event_listener_properties(
       EventListenerClass::kMouseWheel, EventListenerProperties::kBlocking);
-  EXPECT_EQ(
-      EventListenerProperties::kBlocking,
-      host_impl_->GetEventListenerProperties(EventListenerClass::kMouseWheel));
-
-  // But they don't influence the actual handling of the scroll gestures.
   InputHandler::ScrollStatus status =
     host_impl_->ScrollBegin(BeginState(gfx::Point()).get(),
                                    InputHandler::WHEEL);
+  EXPECT_EQ(InputHandler::SCROLL_ON_MAIN_THREAD, status.thread);
+  EXPECT_EQ(MainThreadScrollingReason::kEventHandlers,
+            status.main_thread_scrolling_reasons);
+
+  host_impl_->active_tree()->set_event_listener_properties(
+      EventListenerClass::kMouseWheel,
+      EventListenerProperties::kBlockingAndPassive);
+  status = host_impl_->ScrollBegin(BeginState(gfx::Point()).get(),
+                                   InputHandler::WHEEL);
+  EXPECT_EQ(InputHandler::SCROLL_ON_MAIN_THREAD, status.thread);
+  EXPECT_EQ(MainThreadScrollingReason::kEventHandlers,
+            status.main_thread_scrolling_reasons);
+
+  // But gesture scrolls can still be handled.
+  status = host_impl_->ScrollBegin(BeginState(gfx::Point()).get(),
+                                   InputHandler::TOUCHSCREEN);
   EXPECT_EQ(InputHandler::SCROLL_ON_IMPL_THREAD, status.thread);
   EXPECT_EQ(MainThreadScrollingReason::kNotScrollingOnMain,
+            status.main_thread_scrolling_reasons);
+  host_impl_->ScrollEnd(EndState().get());
+
+  // And if the handlers go away, wheel scrolls can again be processed
+  // on impl.
+  host_impl_->active_tree()->set_event_listener_properties(
+      EventListenerClass::kMouseWheel, EventListenerProperties::kNone);
+  status = host_impl_->ScrollBegin(BeginState(gfx::Point()).get(),
+                                   InputHandler::WHEEL);
+  EXPECT_EQ(InputHandler::SCROLL_ON_IMPL_THREAD, status.thread);
+  EXPECT_EQ(MainThreadScrollingReason::kNotScrollingOnMain,
             status.main_thread_scrolling_reasons);
   host_impl_->ScrollEnd(EndState().get());
 }
 
 TEST_F(LayerTreeHostImplTest, ScrollBlocksOnTouchEventHandlers) {
   LayerImpl* scroll = SetupScrollAndContentsLayers(gfx::Size(100, 100));
   host_impl_->SetViewportSize(gfx::Size(50, 50));
   DrawFrame();
   LayerImpl* root = host_impl_->active_tree()->root_layer();
 
@@ skipping 10023 matching lines @@
 
   // Re-initialize with a software output surface.
   output_surface_ = FakeOutputSurface::CreateSoftware(
       base::WrapUnique(new SoftwareOutputDevice));
   host_impl_->InitializeRenderer(output_surface_.get());
   EXPECT_FALSE(host_impl_->use_gpu_rasterization());
 }
 
 }  // namespace
 }  // namespace cc