Bug 1217715 - Don't limit the system scroll override to the root content. r=botond,masayuki

MozReview-Commit-ID: EH94OR5rEsX

dom/events/WheelHandlingHelper.cpp

@@ -413,12 +413,6 @@ WheelTransaction::OverrideSystemScrollSpeed(WidgetWheelEvent* aEvent)
     return DeltaValues(aEvent);
   }
 
-  // We shouldn't override the scrolling speed on non root scroll frame.
-  if (sTargetFrame !=
-        sTargetFrame->PresContext()->PresShell()->GetRootScrollFrame()) {
-    return DeltaValues(aEvent);
-  }
-
   return DeltaValues(aEvent->OverriddenDeltaX(),
                      aEvent->OverriddenDeltaY());
 }

dom/events/test/test_wheel_default_action.html

@@ -16,9 +16,16 @@
 
 SimpleTest.waitForExplicitFinish();
 SimpleTest.requestFlakyTimeout("untriaged");
+SpecialPowers.pushPrefEnv({"set": [
+    ["mousewheel.system_scroll_override_on_root_content.enabled", false]
+]}, runTest);
 
-var subWin = window.open("window_wheel_default_action.html", "_blank",
-                         "width=500,height=500,scrollbars=yes");
+var subWin = null;
+
+function runTest() {
+  subWin = window.open("window_wheel_default_action.html", "_blank",
+                       "width=500,height=500,scrollbars=yes");
+}
 
 function finish()
 {

gfx/layers/apz/src/AsyncPanZoomController.cpp

@@ -1497,14 +1497,12 @@ AsyncPanZoomController::GetScrollWheelDelta(const ScrollWheelInput& aEvent) cons
 {
   ParentLayerSize scrollAmount;
   ParentLayerSize pageScrollSize;
-  bool isRootContent = false;
 
   {
     // Grab the lock to access the frame metrics.
     ReentrantMonitorAutoEnter lock(mMonitor);
     LayoutDeviceIntSize scrollAmountLD = mScrollMetadata.GetLineScrollAmount();
     LayoutDeviceIntSize pageScrollSizeLD = mScrollMetadata.GetPageScrollAmount();
-    isRootContent = mFrameMetrics.IsRootContent();
     scrollAmount = scrollAmountLD /
       mFrameMetrics.GetDevPixelsPerCSSPixel() * mFrameMetrics.GetZoom();
     pageScrollSize = pageScrollSizeLD /
@@ -1537,9 +1535,9 @@ AsyncPanZoomController::GetScrollWheelDelta(const ScrollWheelInput& aEvent) cons
 
   // For the conditions under which we allow system scroll overrides, see
   // EventStateManager::DeltaAccumulator::ComputeScrollAmountForDefaultAction
-  // and WheelTransaction::OverrideSystemScrollSpeed.
-  if (isRootContent &&
-      gfxPrefs::MouseWheelHasRootScrollDeltaOverride() &&
+  // and WheelTransaction::OverrideSystemScrollSpeed. Note that we do *not*
+  // restrict this to the root content, see bug 1217715 for discussion on this.
+  if (gfxPrefs::MouseWheelHasRootScrollDeltaOverride() &&
       !aEvent.IsCustomizedByUserPrefs() &&
       aEvent.mDeltaType == ScrollWheelInput::SCROLLDELTA_LINE &&
       aEvent.mAllowToOverrideSystemScrollSpeed) {

modules/libpref/init/all.js

@@ -2219,10 +2219,10 @@ pref("mousewheel.acceleration.start", -1);
 // factor to be multiplied for constant acceleration
 pref("mousewheel.acceleration.factor", 10);
 
-// Prefs for override the system mouse wheel scrolling speed on the root
+// Prefs for override the system mouse wheel scrolling speed on
 // content of the web pages.  When
 // "mousewheel.system_scroll_override_on_root_content.enabled" is true and the system
-// scrolling speed isn't customized by the user, the root content scrolling
+// scrolling speed isn't customized by the user, the content scrolling
 // speed is multiplied by the following factors.  The value will be used as
 // 1/100.  E.g., 200 means 2.00.
 // NOTE: Even if "mousewheel.system_scroll_override_on_root_content.enabled" is