Bug 1016035 - Set scroll overflow information on potential swipe start events that have been processed by APZ. r=masayuki

--HG--
extra : commitid : 6mBhLX6HDVv
extra : rebase_source : 4185666bd00b2723cb9d7fbdbc3966a6f429b0fc

dom/events/EventStateManager.cpp

@@ -3132,12 +3132,31 @@ EventStateManager::PostHandleEvent(nsPresContext* aPresContext,
         }
         case WheelPrefs::ACTION_NONE:
         default:
-          // If we don't handle the wheel event, all of the delta values must
-          // be overflown delta values.
+          bool allDeltaOverflown = false;
+          if (wheelEvent->mFlags.mHandledByAPZ) {
+            if (wheelEvent->mCanTriggerSwipe) {
+              // For events that can trigger swipes, APZ needs to know whether
+              // scrolling is possible in the requested direction. It does this
+              // by looking at the scroll overflow values on mCanTriggerSwipe
+              // events after they have been processed.
+              allDeltaOverflown =
+                !ComputeScrollTarget(aTargetFrame, wheelEvent,
+                                     COMPUTE_DEFAULT_ACTION_TARGET);
+            }
+          } else {
+            // The event was processed neither by APZ nor by us, so all of the
+            // delta values must be overflown delta values.
+            allDeltaOverflown = true;
+          }
+
+          if (!allDeltaOverflown) {
+            break;
+          }
           wheelEvent->overflowDeltaX = wheelEvent->deltaX;
           wheelEvent->overflowDeltaY = wheelEvent->deltaY;
           WheelPrefs::GetInstance()->
             CancelApplyingUserPrefsFromOverflowDelta(wheelEvent);
+          wheelEvent->mViewPortIsOverscrolled = true;
           break;
       }
       *aStatus = nsEventStatus_eConsumeNoDefault;