Don't use return value of compositeAndReadbackAsync so it can be void.

content/shell/renderer/test_runner/WebTestProxy.cpp

 // Copyright 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/shell/renderer/test_runner/WebTestProxy.h"
 
 #include <cctype>
 
 #include "base/callback_helpers.h"
 #include "base/debug/trace_event.h"
@@ skipping 470 matching lines @@
 
 void WebTestProxyBase::didCompositeAndReadback(const SkBitmap& bitmap) {
   TRACE_EVENT2("shell",
                "WebTestProxyBase::didCompositeAndReadback",
                "x",
                bitmap.info().fWidth,
                "y",
                bitmap.info().fHeight);
   SkCanvas canvas(bitmap);
   DrawSelectionRect(&canvas);
+  DCHECK(!m_compositeAndReadbackCallback.is_null());
   base::ResetAndReturn(&m_compositeAndReadbackCallback).Run(bitmap);
 }
 
 void WebTestProxyBase::CapturePixelsAsync(
     base::Callback<void(const SkBitmap&)> callback) {
-  m_compositeAndReadbackCallback = callback;
   TRACE_EVENT0("shell", "WebTestProxyBase::CapturePixelsAsync");
 
   // Do a layout here because it might leave compositing mode! x.x
   // TODO(danakj): Remove this when we have kForceCompositingMode everywhere.
   webWidget()->layout();
 
-  if (!webWidget()->compositeAndReadbackAsync(this)) {
+  if (!webWidget()->isAcceleratedCompositingActive()) {
     TRACE_EVENT0("shell",
                  "WebTestProxyBase::CapturePixelsAsync "
-                 "compositeAndReadbackAsync failed");
-    didCompositeAndReadback(SkBitmap());
+                 "isAcceleratedCompositingActive false");
+    callback.Run(SkBitmap());
+    return;
   }
+
+  DCHECK(!callback.is_null());
+  DCHECK(m_compositeAndReadbackCallback.is_null());
+  m_compositeAndReadbackCallback = callback;
+  webWidget()->compositeAndReadbackAsync(this);
 }
 
 void WebTestProxyBase::setLogConsoleOutput(bool enabled)
 {
     m_logConsoleOutput = enabled;
 }
 
 void WebTestProxyBase::paintRect(const WebRect& rect)
 {
     DCHECK(!m_isPainting);
@@ skipping 781 matching lines @@
 
 void WebTestProxyBase::resetInputMethod()
 {
     // If a composition text exists, then we need to let the browser process
     // to cancel the input method's ongoing composition session.
     if (m_webWidget)
         m_webWidget->confirmComposition();
 }
 
 }  // namespace content