Clear renderer compositor trees if new page does not render in 4 seconds

cc/trees/proxy_main.cc

Index: cc/trees/proxy_main.cc
diff --git a/cc/trees/proxy_main.cc b/cc/trees/proxy_main.cc
index bab54a09e88746c6b27e93c5dceef295bfd6f556..0a7a127e052118e4ebbec9929c6d4a59b4bbedf1 100644
--- a/cc/trees/proxy_main.cc
+++ b/cc/trees/proxy_main.cc
@@ -484,4 +484,11 @@ base::SingleThreadTaskRunner* ProxyMain::ImplThreadTaskRunner() {
   return task_runner_provider_->ImplThreadTaskRunner();
 }
 
+void ProxyMain::ResetTrees() {
+  DCHECK(IsMainThread());
+  ImplThreadTaskRunner()->PostTask(
+      FROM_HERE,
+      base::Bind(&ProxyImpl::ResetTrees, base::Unretained(proxy_impl_.get())));
+}
+
 }  // namespace cc