Bug 1835712 - Add a new flag to InputAPZContext to indicate the state we didn't handle the event on the main-thread. r=botond

And use it to tell whether it's safe to inform the handled result to APZ.

Differential Revision: https://phabricator.services.mozilla.com/D180760

gfx/layers/apz/test/mochitest/test_group_touchevents-5.html

@@ -20,12 +20,8 @@ var subtests = [
     ["apz.overscroll.test_async_scroll_offset.enabled", true],
     ["apz.test.logging_enabled", true],
   ]},
-  {"file": "helper_bug1719855.html?prevent=contextmenu", "prefs": [
-    ["android.touch_resampling.enabled", false],
-  ]},
-  {"file": "helper_bug1719855.html", "prefs": [
-    ["android.touch_resampling.enabled", false],
-  ]},
+  {"file": "helper_bug1719855.html?prevent=contextmenu"},
+  {"file": "helper_bug1719855.html"},
   // Add new subtests here. If this starts timing out because it's taking too
   // long, create a test_group_touchevents-6.html file. Refer to 1423011#c57
   // for more details.

gfx/layers/apz/util/InputAPZContext.cpp

@@ -14,6 +14,7 @@ uint64_t InputAPZContext::sBlockId = 0;
 nsEventStatus InputAPZContext::sApzResponse = nsEventStatus_eSentinel;
 bool InputAPZContext::sPendingLayerization = false;
 bool InputAPZContext::sRoutedToChildProcess = false;
+bool InputAPZContext::sDropped = false;
 
 /*static*/
 ScrollableLayerGuid InputAPZContext::GetTargetLayerGuid() { return sGuid; }
@@ -32,6 +33,9 @@ bool InputAPZContext::WasRoutedToChildProcess() {
   return sRoutedToChildProcess;
 }
 
+/*static*/
+bool InputAPZContext::WasDropped() { return sDropped; }
+
 InputAPZContext::InputAPZContext(const ScrollableLayerGuid& aGuid,
                                  const uint64_t& aBlockId,
                                  const nsEventStatus& aApzResponse,
@@ -40,12 +44,14 @@ InputAPZContext::InputAPZContext(const ScrollableLayerGuid& aGuid,
       mOldBlockId(sBlockId),
       mOldApzResponse(sApzResponse),
       mOldPendingLayerization(sPendingLayerization),
-      mOldRoutedToChildProcess(sRoutedToChildProcess) {
+      mOldRoutedToChildProcess(sRoutedToChildProcess),
+      mOldDropped(sDropped) {
   sGuid = aGuid;
   sBlockId = aBlockId;
   sApzResponse = aApzResponse;
   sPendingLayerization = aPendingLayerization;
   sRoutedToChildProcess = false;
+  sDropped = false;
 }
 
 InputAPZContext::~InputAPZContext() {
@@ -54,6 +60,7 @@ InputAPZContext::~InputAPZContext() {
   sApzResponse = mOldApzResponse;
   sPendingLayerization = mOldPendingLayerization;
   sRoutedToChildProcess = mOldRoutedToChildProcess;
+  sDropped = mOldDropped;
 }
 
 /*static*/
@@ -61,5 +68,8 @@ void InputAPZContext::SetRoutedToChildProcess() {
   sRoutedToChildProcess = true;
 }
 
+/*static*/
+void InputAPZContext::SetDropped() { sDropped = true; }
+
 }  // namespace layers
 }  // namespace mozilla

gfx/layers/apz/util/InputAPZContext.h

@@ -34,6 +34,9 @@ class MOZ_STACK_CLASS InputAPZContext {
 
   // State that is set in deeper code and propagated upwards.
   static bool sRoutedToChildProcess;
+  // True if the WidgetInputEvent was dropped (which means the event wasn't
+  // dispatched) on the main-thread.
+  static bool sDropped;
 
  public:
   // Functions to access downwards-propagated data
@@ -45,6 +48,8 @@ class MOZ_STACK_CLASS InputAPZContext {
   // Functions to access upwards-propagated data
   static bool WasRoutedToChildProcess();
 
+  static bool WasDropped();
+
   // Constructor sets the data to be propagated downwards
   InputAPZContext(const ScrollableLayerGuid& aGuid, const uint64_t& aBlockId,
                   const nsEventStatus& aApzResponse,
@@ -53,6 +58,7 @@ class MOZ_STACK_CLASS InputAPZContext {
 
   // Functions to set data to be propagated upwards
   static void SetRoutedToChildProcess();
+  static void SetDropped();
 
  private:
   ScrollableLayerGuid mOldGuid;
@@ -61,6 +67,7 @@ class MOZ_STACK_CLASS InputAPZContext {
   bool mOldPendingLayerization;
 
   bool mOldRoutedToChildProcess;
+  bool mOldDropped;
 };
 
 }  // namespace layers

layout/base/TouchManager.cpp

@@ -10,6 +10,7 @@
 #include "mozilla/dom/Document.h"
 #include "mozilla/dom/EventTarget.h"
 #include "mozilla/PresShell.h"
+#include "mozilla/layers/InputAPZContext.h"
 #include "nsIContent.h"
 #include "nsIFrame.h"
 #include "nsLayoutUtils.h"
@@ -328,6 +329,10 @@ bool TouchManager::PreHandleEvent(WidgetEvent* aEvent, nsEventStatus* aStatus,
             }
           }
         } else {
+          // This touch event isn't going to be dispatched on the main-thread,
+          // we need to tell it to APZ because returned nsEventStatus is
+          // unreliable to tell whether the event was preventDefaulted or not.
+          layers::InputAPZContext::SetDropped();
           return false;
         }
       }

widget/nsBaseWidget.cpp

@@ -1092,8 +1092,10 @@ nsEventStatus nsBaseWidget::ProcessUntransformedAPZEvent(
   UniquePtr<WidgetEvent> original(aEvent->Duplicate());
   DispatchEvent(aEvent, status);
 
-  if (mAPZC && !InputAPZContext::WasRoutedToChildProcess() && inputBlockId) {
-    // EventStateManager did not route the event into the child process.
+  if (mAPZC && !InputAPZContext::WasRoutedToChildProcess() &&
+      !InputAPZContext::WasDropped() && inputBlockId) {
+    // EventStateManager did not route the event into the child process and
+    // the event was dispatched in the parent process.
     // It's safe to communicate to APZ that the event has been processed.
     // Note that here aGuid.mLayersId might be different from
     // mCompositorSession->RootLayerTreeId() because the event might have gotten