Implement Middle Click Autoscroll on all platforms not just Windows

third_party/WebKit/Source/core/input/EventHandler.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2006 Alexey Proskuryakov (ap@webkit.org)
  * Copyright (C) 2012 Digia Plc. and/or its subsidiary(-ies)
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
@@ skipping 418 matching lines @@
 
 WebInputEventResult EventHandler::handleMouseReleaseEvent(const MouseEventWithHitTestResults& event)
 {
     AutoscrollController* controller = m_scrollManager.autoscrollController();
     if (controller && controller->autoscrollInProgress())
         m_scrollManager.stopAutoscroll();
 
     return selectionController().handleMouseReleaseEvent(event, m_dragStartPos) ? WebInputEventResult::HandledSystem : WebInputEventResult::NotHandled;
 }
 
-#if OS(WIN)
-
 void EventHandler::startPanScrolling(LayoutObject* layoutObject)
 {
     if (!layoutObject->isBox())
         return;
     AutoscrollController* controller = m_scrollManager.autoscrollController();
     if (!controller)
         return;
     controller->startPanScrolling(toLayoutBox(layoutObject), lastKnownMousePosition());
     invalidateClick();
 }
 
-#endif // OS(WIN)
-
 HitTestResult EventHandler::hitTestResultAtPoint(const LayoutPoint& point, HitTestRequest::HitTestRequestType hitType, const LayoutSize& padding)
 {
     TRACE_EVENT0("blink", "EventHandler::hitTestResultAtPoint");
 
     ASSERT((hitType & HitTestRequest::ListBased) || padding.isEmpty());
 
     // We always send hitTestResultAtPoint to the main frame if we have one,
     // otherwise we might hit areas that are obscured by higher frames.
     if (m_frame->page()) {
         LocalFrame* mainFrame = m_frame->localFrameRoot();
@@ skipping 360 matching lines @@
         // has been handled. See crbug.com/269917
         m_capturesDragging = subframe->eventHandler().capturesDragging();
         if (m_mousePressed && m_capturesDragging) {
             m_capturingMouseEventsNode = mev.innerNode();
             m_eventHandlerWillResetCapturingMouseEventsNode = true;
         }
         invalidateClick();
         return result;
     }
 
-#if OS(WIN)
-    // We store whether pan scrolling is in progress before calling stopAutoscroll()
-    // because it will set m_autoscrollType to NoAutoscroll on return.
-    bool isPanScrollInProgress = m_scrollManager.panScrollInProgress();
-    m_scrollManager.stopAutoscroll();
-    if (isPanScrollInProgress) {
-        // We invalidate the click when exiting pan scrolling so that we don't inadvertently navigate
-        // away from the current page (e.g. the click was on a hyperlink). See <rdar://problem/6095023>.
-        invalidateClick();
-        return WebInputEventResult::HandledSuppressed;
+    if (RuntimeEnabledFeatures::panScrollingEnabled()) {
+        // We store whether pan scrolling is in progress before calling stopAutoscroll()
+        // because it will set m_autoscrollType to NoAutoscroll on return.
+        bool isPanScrollInProgress = m_scrollManager.panScrollInProgress();
+        m_scrollManager.stopAutoscroll();
+        if (isPanScrollInProgress) {
+            // We invalidate the click when exiting pan scrolling so that we don't inadvertently navigate
+            // away from the current page (e.g. the click was on a hyperlink). See <rdar://problem/6095023>.
+            invalidateClick();
+            updatePointerTargetAndDispatchEvents(EventTypeNames::mousedown, mev.innerNode(), m_clickCount, mev.event());

[sunyunjia, 2016/09/01 01:50:31]

I'm not sure the side effects of adding this line of code. But it helps to solve
crbug.com/548226 as well.

[Navid Zolghadr, 2016/09/02 17:36:57]

When pan is enabled and that pan circle is shown, if you press left mouse button
this used to go to this if and disable the pan (and not send a mousedown to the
page) and when you would release the mouse it would send a mouseup to the page. 
You are now changing that behavior to also send that mousedown that we were
suppressing before. Just wanted to point that out and whether that is the
intention or not. Also in that case do we like to send the click events for
these mousedown/ups?

Also I noticed something when I was playing with pan on Windows. If I'm in pan
mode, and middle click again that also disables the pan. Does it do that after
this patch on Linux or does it remain in pan mode?

+            return WebInputEventResult::HandledSuppressed;
+        }
     }
-#endif
 
     m_clickCount = mouseEvent.clickCount();
     m_clickNode = mev.innerNode()->isTextNode() ?  FlatTreeTraversal::parent(*mev.innerNode()) : mev.innerNode();
 
     if (!mouseEvent.fromTouch())
         m_frame->selection().setCaretBlinkingSuspended(true);
 
     WebInputEventResult eventResult = updatePointerTargetAndDispatchEvents(EventTypeNames::mousedown, mev.innerNode(), m_clickCount, mev.event());
 
     if (eventResult == WebInputEventResult::NotHandled && m_frame->view()) {
@@ skipping 250 matching lines @@
     if (!mouseEvent.fromTouch())
         m_frame->selection().setCaretBlinkingSuspended(false);
 
     std::unique_ptr<UserGestureIndicator> gestureIndicator;
 
     if (m_frame->localFrameRoot()->eventHandler().m_lastMouseDownUserGestureToken)
         gestureIndicator = wrapUnique(new UserGestureIndicator(m_frame->localFrameRoot()->eventHandler().m_lastMouseDownUserGestureToken.release()));
     else
         gestureIndicator = wrapUnique(new UserGestureIndicator(DefinitelyProcessingUserGesture));
 
-#if OS(WIN)
-    if (Page* page = m_frame->page())
-        page->autoscrollController().handleMouseReleaseForPanScrolling(m_frame, mouseEvent);
-#endif
+    if (RuntimeEnabledFeatures::panScrollingEnabled()) {
+        if (Page* page = m_frame->page())
+            page->autoscrollController().handleMouseReleaseForPanScrolling(m_frame, mouseEvent);
+    }
 
     m_mousePressed = false;
     setLastKnownMousePosition(mouseEvent);
 
     if (m_svgPan) {
         m_svgPan = false;
         m_frame->document()->accessSVGExtensions().updatePan(m_frame->view()->rootFrameToContents(m_lastKnownMousePosition));
         return WebInputEventResult::HandledSuppressed;
     }
 
@@ skipping 1476 matching lines @@
 
 FrameHost* EventHandler::frameHost() const
 {
     if (!m_frame->page())
         return nullptr;
 
     return &m_frame->page()->frameHost();
 }
 
 } // namespace blink