Main thread Scrollbar interaction injects GSB/GSU/GSE to compositor

If Scroll Unification is enabled, send GSB, GSU and GSE to
CompositorThreadEventQueue instead of MainThreadEventQueue in
|WebFrameWidgetBase::InjectGestureScrollEvent|.


Bug: 1047198
Change-Id: Iec178bf6053d937ed1b6cdd977ac7e42267b4ef2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2392409
Commit-Queue: Liviu Tinta <liviutinta@chromium.org>
Reviewed-by: David Bokan <bokan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#808052}

third_party/blink/renderer/core/frame/web_frame_widget_base.cc

@@ -1713,8 +1713,26 @@ void WebFrameWidgetBase::InjectGestureScrollEvent(
     ui::ScrollGranularity granularity,
     cc::ElementId scrollable_area_element_id,
     blink::WebInputEvent::Type injected_type) {
-  widget_base_->input_handler().InjectGestureScrollEvent(
-      device, delta, granularity, scrollable_area_element_id, injected_type);
+  if (RuntimeEnabledFeatures::ScrollUnificationEnabled()) {
+    // create a GestureScroll Event and post it to the compositor thread
+    // TODO(crbug.com/1126098) use original input event's timestamp.
+    // TODO(crbug.com/1082590) ensure continuity in scroll metrics collection
+    base::TimeTicks now = base::TimeTicks::Now();
+    std::unique_ptr<WebGestureEvent> gesture_event =
+        WebGestureEvent::GenerateInjectedScrollGesture(
+            injected_type, now, device, gfx::PointF(0, 0), delta, granularity);
+    if (injected_type == WebInputEvent::Type::kGestureScrollBegin) {
+      gesture_event->data.scroll_begin.scrollable_area_element_id =
+          scrollable_area_element_id.GetStableId();
+      gesture_event->data.scroll_begin.main_thread_hit_tested = true;
+    }
+
+    widget_base_->widget_input_handler_manager()
+        ->DispatchScrollGestureToCompositor(std::move(gesture_event));
+  } else {
+    widget_base_->input_handler().InjectGestureScrollEvent(
+        device, delta, granularity, scrollable_area_element_id, injected_type);
+  }
 }
 
 void WebFrameWidgetBase::DidChangeCursor(const ui::Cursor& cursor) {

third_party/blink/renderer/platform/widget/input/widget_input_handler_manager.cc

@@ -8,6 +8,7 @@
 
 #include "base/bind.h"
 #include "base/check_op.h"
+#include "base/feature_list.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/notreached.h"
 #include "cc/base/features.h"
@@ -389,6 +390,27 @@ void WidgetInputHandlerManager::LogInputTimingUMA() {
   }
 }
 
+void WidgetInputHandlerManager::DispatchScrollGestureToCompositor(
+    std::unique_ptr<WebGestureEvent> event) {
+  DCHECK(base::FeatureList::IsEnabled(features::kScrollUnification));
+  std::unique_ptr<WebCoalescedInputEvent> web_scoped_gesture_event =
+      std::make_unique<WebCoalescedInputEvent>(std::move(event),
+                                               ui::LatencyInfo());
+  DCHECK(compositor_task_runner_);
+  compositor_task_runner_->PostTask(
+      FROM_HERE, base::BindOnce(&WidgetInputHandlerManager::
+                                    HandleInputEventWithLatencyInfoOnCompositor,
+                                this, std::move(web_scoped_gesture_event)));
+}
+
+void WidgetInputHandlerManager::HandleInputEventWithLatencyInfoOnCompositor(
+    std::unique_ptr<WebCoalescedInputEvent> event) {
+  DCHECK(base::FeatureList::IsEnabled(features::kScrollUnification));
+  DCHECK(input_handler_proxy_);
+  input_handler_proxy_->HandleInputEventWithLatencyInfo(std::move(event),
+                                                        base::DoNothing());
+}
+
 void WidgetInputHandlerManager::DispatchEvent(
     std::unique_ptr<WebCoalescedInputEvent> event,
     mojom::blink::WidgetInputHandler::DispatchEventCallback callback) {
@@ -398,7 +420,7 @@ void WidgetInputHandlerManager::DispatchEvent(
   if (!event_is_move)
     LogInputTimingUMA();
 
-  // Drop input if we are deferring a rendring pipeline phase, unless it's a
+  // Drop input if we are deferring a rendering pipeline phase, unless it's a
   // move event.
   // We don't want users interacting with stuff they can't see, so we drop it.
   // We allow moves because we need to keep the current pointer location up
@@ -436,7 +458,7 @@ void WidgetInputHandlerManager::DispatchEvent(
       return;
     }
 
-    // The InputHandlerProxy will be the first to try handing the event on the
+    // The InputHandlerProxy will be the first to try handling the event on the
     // compositor thread. It will respond to this class by calling
     // DidHandleInputEventSentToCompositor with the result of its attempt. Based
     // on the resulting disposition, DidHandleInputEventSentToCompositor will

third_party/blink/renderer/platform/widget/input/widget_input_handler_manager.h

@@ -98,6 +98,8 @@ class PLATFORM_EXPORT WidgetInputHandlerManager final
       const WebGestureEvent& gesture_event,
       const cc::InputHandlerScrollResult& scroll_result);
 
+  void DispatchScrollGestureToCompositor(
+      std::unique_ptr<WebGestureEvent> event);
   void DispatchEvent(
       std::unique_ptr<blink::WebCoalescedInputEvent> event,
       mojom::blink::WidgetInputHandler::DispatchEventCallback callback);
@@ -225,6 +227,9 @@ class PLATFORM_EXPORT WidgetInputHandlerManager final
       const WebGestureEvent& gesture_event,
       const cc::InputHandlerScrollResult& scroll_result);
 
+  void HandleInputEventWithLatencyInfoOnCompositor(
+      std::unique_ptr<WebCoalescedInputEvent>);
+
   // Returns the task runner for the thread that receives input. i.e. the
   // "Mojo-bound" thread.
   const scoped_refptr<base::SingleThreadTaskRunner>& InputThreadTaskRunner()

third_party/blink/web_tests/TestExpectations

@@ -6731,3 +6731,9 @@ crbug.com/1126709 [ Win ] virtual/threaded/external/wpt/animation-worklet/workle
 
 # Sheriff 2020-09-17
 crbug.com/1129347 [ Mac10.13 Debug ] http/tests/devtools/persistence/persistence-external-change-breakpoints.js [ Pass Failure ]
+### virtual/scroll-unification/fast/scrolling/scrollbars/
+virtual/scroll-unification/fast/scrolling/scrollbars/mouse-autoscrolling-on-scrollbar.html [ Failure ]
+virtual/scroll-unification/fast/scrolling/scrollbars/mouse-scrolling-on-div-scrollbar.html [ Failure ]
+virtual/scroll-unification/fast/scrolling/scrollbars/scrollbar-occluded-by-div.html [ Failure ]
+virtual/scroll-unification/fast/scrolling/scrollbars/scrollbar-rtl-manipulation.html [ Failure ]
+virtual/scroll-unification/fast/scrolling/scrollbars/dsf-ready/mouse-interactions-dsf-2.html [ Failure ]

third_party/blink/web_tests/VirtualTestSuites

@@ -743,5 +743,11 @@
     "args": ["--enable-threaded-compositing",
              "--enable-features=CompositeCrossOriginIframes",
              "--disable-auto-wpt-origin-isolation"]
+  },
+  {
+    "prefix": "scroll-unification",
+    "bases": ["fast/scrolling/scrollbars"],
+    "args": ["--enable-features=ScrollUnification",
+             "--enable-threaded-compositing"]
   }
 ]

third_party/blink/web_tests/virtual/scroll-unification/README.md

+This directory is dedicated for testing the "ScrollUnification" feature.

third_party/blink/web_tests/virtual/scroll-unification/README.txt

+This directory is dedicated for testing the "ScrollUnification" feature.