Bug 951793 - Obey overscroll-behavior for any overscroll effect. r=kats

MozReview-Commit-ID: HyATx3aCmmm

--HG--
extra : rebase_source : 43f8d69a8e10f778179e77679cb7581b95d25b87

gfx/layers/apz/src/AsyncPanZoomController.cpp

@@ -2809,8 +2809,8 @@ void AsyncPanZoomController::OverscrollBy(ParentLayerPoint& aOverscroll) {
   bool xConsumed = FuzzyEqualsAdditive(aOverscroll.x, 0.0f, COORDINATE_EPSILON);
   bool yConsumed = FuzzyEqualsAdditive(aOverscroll.y, 0.0f, COORDINATE_EPSILON);
 
-  bool shouldOverscrollX = xCanScroll && !xConsumed;
-  bool shouldOverscrollY = yCanScroll && !yConsumed;
+  bool shouldOverscrollX = xCanScroll && !xConsumed && mX.OverscrollBehaviorAllowsOverscrollEffect();
+  bool shouldOverscrollY = yCanScroll && !yConsumed && mY.OverscrollBehaviorAllowsOverscrollEffect();
 
   mOverscrollEffect->ConsumeOverscroll(aOverscroll, shouldOverscrollX, shouldOverscrollY);
 }
@@ -2892,7 +2892,18 @@ void AsyncPanZoomController::HandleFlingOverscroll(const ParentLayerPoint& aVelo
                                          aScrolledApzc};
     ParentLayerPoint residualVelocity = treeManagerLocal->DispatchFling(this, handoffState);
     if (!IsZero(residualVelocity) && IsPannable() && gfxPrefs::APZOverscrollEnabled()) {
-      mOverscrollEffect->HandleFlingOverscroll(residualVelocity);
+      // Obey overscroll-behavior.
+      RecursiveMutexAutoLock lock(mRecursiveMutex);
+      if (!mX.OverscrollBehaviorAllowsOverscrollEffect()) {
+        residualVelocity.x = 0;
+      }
+      if (!mY.OverscrollBehaviorAllowsOverscrollEffect()) {
+        residualVelocity.y = 0;
+      }
+
+      if (!IsZero(residualVelocity)) {
+        mOverscrollEffect->HandleFlingOverscroll(residualVelocity);
+      }
     }
   }
 }