Fix crash in taking a screenshot of a closed popup

content/renderer/gpu/render_widget_compositor.cc

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/renderer/gpu/render_widget_compositor.h"
 
 #include <limits>
 #include <string>
 
 #include "base/command_line.h"
@@ skipping 687 matching lines @@
   }
 }
 
 void RenderWidgetCompositor::compositeAndReadbackAsync(
     blink::WebCompositeAndReadbackAsyncCallback* callback) {
   DCHECK(!temporary_copy_output_request_);
   temporary_copy_output_request_ =
       cc::CopyOutputRequest::CreateBitmapRequest(
           base::Bind(&CompositeAndReadbackAsyncCallback, callback));
   // Force a commit to happen. The temporary copy output request will
-  // be installed after layout which will happen as a part of the commit, when
-  // there is guaranteed to be a root layer.
+  // be installed after layout which will happen as a part of the commit, for
+  // widgets that delay the creation of their output surface.
   bool threaded = !!compositor_deps_->GetCompositorImplThreadTaskRunner().get();
   if (!threaded &&
       !layer_tree_host_->settings().single_thread_proxy_scheduler) {
     layer_tree_host_->Composite(gfx::FrameTime::Now());
   } else {
     layer_tree_host_->SetNeedsCommit();
   }
 }
 
 void RenderWidgetCompositor::finishAllRendering() {
@@ skipping 71 matching lines @@
 }
 
 void RenderWidgetCompositor::BeginMainFrameNotExpectedSoon() {
   compositor_deps_->GetRendererScheduler()->BeginFrameNotExpectedSoon();
 }
 
 void RenderWidgetCompositor::Layout() {
   widget_->webwidget()->layout();
 
   if (temporary_copy_output_request_) {
-    DCHECK(layer_tree_host_->root_layer());
-    layer_tree_host_->root_layer()->RequestCopyOfOutput(
-        temporary_copy_output_request_.Pass());
+    // For WebViewImpl, this will always have a root layer.  For other widgets,
+    // the widget may be closed before servicing this request, so ignore it.
+    if (cc::Layer* root_layer = layer_tree_host_->root_layer()) {
+      root_layer->RequestCopyOfOutput(temporary_copy_output_request_.Pass());
+    } else {
+      temporary_copy_output_request_->SendEmptyResult();
+      temporary_copy_output_request_ = nullptr;
+    }
   }
 }
 
 void RenderWidgetCompositor::ApplyViewportDeltas(
     const gfx::Vector2dF& inner_delta,
     const gfx::Vector2dF& outer_delta,
     const gfx::Vector2dF& elastic_overscroll_delta,
     float page_scale,
     float top_controls_delta) {
   widget_->webwidget()->applyViewportDeltas(
@@ skipping 96 matching lines @@
   cc::ContextProvider* provider =
       compositor_deps_->GetSharedMainThreadContextProvider();
   // provider can be NULL after the GPU process crashed enough times and we
   // don't want to restart it any more (falling back to software).
   if (!provider)
     return;
   provider->ContextGL()->RateLimitOffscreenContextCHROMIUM();
 }
 
 }  // namespace content