Bug 1507068 - Ensure mParent is not null in mozilla::layers::CompositorBridgeParent::GetAndroidDynamicToolbarAnimator r=snorp,kats

Speculative fix for Bug 1507068. Checks if mParent is not null before trying to get a pointer to the toolbar animator

Differential Revision: https://phabricator.services.mozilla.com/D11957

--HG--
extra : moz-landing-system : lando

gfx/layers/ipc/UiCompositorControllerParent.cpp

@@ -300,6 +300,9 @@ UiCompositorControllerParent::Initialize()
   LayerTreeState* state = CompositorBridgeParent::GetIndirectShadowTree(mRootLayerTreeId);
   MOZ_ASSERT(state);
   MOZ_ASSERT(state->mParent);
+  if (!state->mParent) {
+    return;
+  }
   state->mUiControllerParent = this;
 #if defined(MOZ_WIDGET_ANDROID)
   AndroidDynamicToolbarAnimator* animator = state->mParent->GetAndroidDynamicToolbarAnimator();