Bug 915385 - Add a hidden pref for disabling apz zoom. r=kats

gfx/layers/ipc/AsyncPanZoomController.cpp

@@ -142,12 +142,18 @@ static float gYStationarySizeMultiplier = 2.5f;
  */
 
 static int gAsyncScrollThrottleTime = 100;
+
 /**
  * The timeout in ms for mAsyncScrollTimeoutTask delay task.
  * Default is 300ms if there is no "apzc.asyncscroll.timeout" in preference.
  */
 static int gAsyncScrollTimeout = 300;
 
+/**
+ * Temporary pref for disabling zoom in metrofx on aurora.
+ */
+static bool gAsyncZoomDisabled = false;
+
 static TimeStamp sFrameTime;
 
 static TimeStamp
@@ -185,6 +191,7 @@ AsyncPanZoomController::InitializeGlobalState()
   Preferences::AddFloatVarCache(&gYStationarySizeMultiplier, "gfx.azpc.y_stationary_size_multiplier", gYStationarySizeMultiplier);
   Preferences::AddIntVarCache(&gAsyncScrollThrottleTime, "apzc.asyncscroll.throttle", gAsyncScrollThrottleTime);
   Preferences::AddIntVarCache(&gAsyncScrollTimeout, "apzc.asyncscroll.timeout", gAsyncScrollTimeout);
+  Preferences::AddBoolVarCache(&gAsyncZoomDisabled, "apzc.asynczoom.disabled", gAsyncZoomDisabled);
 
   gComputedTimingFunction = new ComputedTimingFunction();
   gComputedTimingFunction->Init(
@@ -221,6 +228,9 @@ AsyncPanZoomController::AsyncPanZoomController(uint64_t aLayersId,
   if (aGestures == USE_GESTURE_DETECTOR) {
     mGestureEventListener = new GestureEventListener(this);
   }
+  if (gAsyncZoomDisabled) {
+    mAllowZoom = false;
+  }
 }
 
 AsyncPanZoomController::~AsyncPanZoomController() {
@@ -1363,6 +1373,9 @@ void AsyncPanZoomController::SetZoomAndResolution(const CSSToScreenScale& aZoom)
 void AsyncPanZoomController::UpdateZoomConstraints(bool aAllowZoom,
                                                    const CSSToScreenScale& aMinZoom,
                                                    const CSSToScreenScale& aMaxZoom) {
+  if (gAsyncZoomDisabled) {
+    return;
+  }
   mAllowZoom = aAllowZoom;
   mMinZoom = (MIN_ZOOM > aMinZoom ? MIN_ZOOM : aMinZoom);
   mMaxZoom = (MAX_ZOOM > aMaxZoom ? aMaxZoom : MAX_ZOOM);