Fix race conditions in window snapshot code.

content/renderer/gpu/render_widget_compositor.cc

Index: content/renderer/gpu/render_widget_compositor.cc
diff --git a/content/renderer/gpu/render_widget_compositor.cc b/content/renderer/gpu/render_widget_compositor.cc
index 2ee9f7590f8d5af00179f7488a0c8c0835047dcf..cc7c6af943b4b405490ae534bc8feb7c9717f350 100644
--- a/content/renderer/gpu/render_widget_compositor.cc
+++ b/content/renderer/gpu/render_widget_compositor.cc
@@ -379,6 +379,17 @@ const cc::Layer* RenderWidgetCompositor::GetRootLayer() const {
   return layer_tree_host_->root_layer();
 }
 
+void RenderWidgetCompositor::SetNeedsForcedRedraw() {
+  layer_tree_host_->SetNextCommitForcesRedraw();
+  if (threaded_) {
+    LOG(INFO) << "RenderWidgetCompositor::SetNeedsForcedRedraw: threaded";
+    layer_tree_host_->SetNeedsAnimate();
+  } else {
+    LOG(INFO) << "RenderWidgetCompositor::SetNeedsForcedRedraw: not threaded";
+    widget_->scheduleAnimation();
+  }
+}
+
 bool RenderWidgetCompositor::initialize(cc::LayerTreeSettings settings) {
   scoped_refptr<base::MessageLoopProxy> compositor_message_loop_proxy =
       RenderThreadImpl::current()->compositor_message_loop_proxy();