Added early out for pinch to prevent crash when no inner scroll layer.

cc/trees/layer_tree_host_impl.cc

Index: cc/trees/layer_tree_host_impl.cc
diff --git a/cc/trees/layer_tree_host_impl.cc b/cc/trees/layer_tree_host_impl.cc
index ec89ddcfd734a055a9cdc9fa4dd9bc60bc870f99..1773e6bb5cb069b5966d0fc7cb8179f548b7609d 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -2508,9 +2508,10 @@ void LayerTreeHostImpl::PinchGestureBegin() {
 
 void LayerTreeHostImpl::PinchGestureUpdate(float magnify_delta,
                                            gfx::Point anchor) {
-  TRACE_EVENT0("cc", "LayerTreeHostImpl::PinchGestureUpdate");
+  if (!InnerViewportScrollLayer())
+    return;
 
-  DCHECK(InnerViewportScrollLayer());
+  TRACE_EVENT0("cc", "LayerTreeHostImpl::PinchGestureUpdate");
 
   // Keep the center-of-pinch anchor specified by (x, y) in a stable
   // position over the course of the magnify.