Bug 1466208 - part 26: Create PresShell::EventHandler::EventTargetData::UpdateTouchEventTarget() r=smaug

After dispatching pointer events, `PresShell::EventHandler::HandleEvent()`
updates event target only when the event is a touch event.  We should do it in
a new method of `EventTargetData`.

Although I don't know why this is done in
`PresShell::EventHandler::DispatchPrecedingPointerEvent()`.

Differential Revision: https://phabricator.services.mozilla.com/D21192

--HG--
extra : moz-landing-system : lando

layout/base/PresShell.cpp

@@ -6659,22 +6659,10 @@ nsresult PresShell::EventHandler::HandleEvent(nsIFrame* aFrame,
     }
 
     // frame could be null after dispatching pointer events.
-    if (aGUIEvent->mClass == eTouchEventClass) {
-      if (aGUIEvent->mMessage == eTouchStart) {
-        WidgetTouchEvent* touchEvent = aGUIEvent->AsTouchEvent();
-        if (nsIFrame* newFrame =
-                TouchManager::SuppressInvalidPointsAndGetTargetedFrame(
-                    touchEvent)) {
-          eventTargetData.SetFrameAndComputePresShellAndContent(newFrame,
-                                                                aGUIEvent);
-        }
-      } else if (PresShell* newShell =
-                     PresShell::GetShellForTouchEvent(aGUIEvent)) {
-        // Touch events (except touchstart) are dispatching to the captured
-        // element. Get correct shell from it.
-        eventTargetData.mPresShell = newShell;
-      }
-    }
+    // XXX Despite of this comment, we update the event target data outside
+    //     DispatchPrecedingPointerEvent().  Can we make it call
+    //     UpdateTouchEventTarget()?
+    eventTargetData.UpdateTouchEventTarget(aGUIEvent);
 
     // Handle the event in the correct shell.
     // We pass the subshell's root frame as the frame to start from. This is
@@ -10865,3 +10853,32 @@ bool PresShell::EventHandler::EventTargetData::ComputeElementFromFrame(
   // If we found an element, target it.  Otherwise, target *nothing*.
   return !!mContent;
 }
+
+void PresShell::EventHandler::EventTargetData::UpdateTouchEventTarget(
+    WidgetGUIEvent* aGUIEvent) {
+  MOZ_ASSERT(aGUIEvent);
+
+  if (aGUIEvent->mClass != eTouchEventClass) {
+    return;
+  }
+
+  if (aGUIEvent->mMessage == eTouchStart) {
+    WidgetTouchEvent* touchEvent = aGUIEvent->AsTouchEvent();
+    nsIFrame* newFrame =
+        TouchManager::SuppressInvalidPointsAndGetTargetedFrame(touchEvent);
+    if (!newFrame) {
+      return;  // XXX Why don't we stop handling the event in this case?
+    }
+    SetFrameAndComputePresShellAndContent(newFrame, aGUIEvent);
+    return;
+  }
+
+  PresShell* newPresShell = PresShell::GetShellForTouchEvent(aGUIEvent);
+  if (!newPresShell) {
+    return;  // XXX Why don't we stop handling the event in this case?
+  }
+
+  // Touch events (except touchstart) are dispatching to the captured
+  // element. Get correct shell from it.
+  mPresShell = newPresShell;
+}

layout/base/PresShell.h

@@ -639,6 +639,15 @@ class PresShell final : public nsIPresShell,
        */
       bool ComputeElementFromFrame(WidgetGUIEvent* aGUIEvent);
 
+      /**
+       * UpdateTouchEventTarget() updates mFrame, mPresShell and mContent if
+       * aGUIEvent is a touch event and there is new proper target.
+       *
+       * @param aGUIEvent       The handled event.  If it's not a touch event,
+       *                        this method does nothing.
+       */
+      void UpdateTouchEventTarget(WidgetGUIEvent* aGUIEvent);
+
       RefPtr<PresShell> mPresShell;
       nsIFrame* mFrame;
       nsCOMPtr<nsIContent> mContent;