Bug 1127066 - Complain loudly if APZEventState is used with a widget that doesn't support weak references. r=kats

--HG--
extra : source : e4337bd21059a0ecbffa5d0d567dd9a8f0a3bcd1

gfx/layers/apz/util/APZEventState.cpp

@@ -25,7 +25,7 @@ static bool sActiveDurationMsSet = false;
 
 APZEventState::APZEventState(nsIWidget* aWidget,
                              const nsRefPtr<ContentReceivedInputBlockCallback>& aCallback)
-  : mWidget(do_GetWeakReference(aWidget))
+  : mWidget(nullptr)  // initialized in constructor body
   , mActiveElementManager(new ActiveElementManager())
   , mContentReceivedInputBlockCallback(aCallback)
   , mPendingTouchPreventedResponse(false)
@@ -33,6 +33,11 @@ APZEventState::APZEventState(nsIWidget* aWidget,
   , mEndTouchIsClick(false)
   , mTouchEndCancelled(false)
 {
+  nsresult rv;
+  mWidget = do_GetWeakReference(aWidget, &rv);
+  MOZ_ASSERT(NS_SUCCEEDED(rv), "APZEventState constructed with a widget that"
+      " does not support weak references. APZ will NOT work!");
+
   if (!sActiveDurationMsSet) {
     Preferences::AddIntVarCache(&sActiveDurationMs,
                                 "ui.touch_activation.duration_ms",