Implement Middle Click Autoscroll on all platforms not just Windows

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

Index: third_party/WebKit/Source/core/input/EventHandler.cpp
diff --git a/third_party/WebKit/Source/core/input/EventHandler.cpp b/third_party/WebKit/Source/core/input/EventHandler.cpp
index b3d05d79c33807ff153a024ffc3580ff1cc56a87..bc8a2511ace99d0061e2acfde50c867b601112c3 100644
--- a/third_party/WebKit/Source/core/input/EventHandler.cpp
+++ b/third_party/WebKit/Source/core/input/EventHandler.cpp
@@ -436,8 +436,6 @@ WebInputEventResult EventHandler::handleMouseReleaseEvent(const MouseEventWithHi
     return selectionController().handleMouseReleaseEvent(event, m_dragStartPos) ? WebInputEventResult::HandledSystem : WebInputEventResult::NotHandled;
 }
 
-#if OS(WIN)
-
 void EventHandler::startPanScrolling(LayoutObject* layoutObject)
 {
     if (!layoutObject->isBox())
@@ -449,8 +447,6 @@ void EventHandler::startPanScrolling(LayoutObject* layoutObject)
     invalidateClick();
 }
 
-#endif // OS(WIN)
-
 HitTestResult EventHandler::hitTestResultAtPoint(const LayoutPoint& point, HitTestRequest::HitTestRequestType hitType, const LayoutSize& padding)
 {
     TRACE_EVENT0("blink", "EventHandler::hitTestResultAtPoint");
@@ -831,18 +827,19 @@ WebInputEventResult EventHandler::handleMousePressEvent(const PlatformMouseEvent
         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();
@@ -1113,10 +1110,10 @@ WebInputEventResult EventHandler::handleMouseReleaseEvent(const PlatformMouseEve
     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);