WebTestProxy should explode if readback requests are unhandled

content/shell/renderer/test_runner/web_test_proxy.cc

 // Copyright 2014 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/web_test_proxy.h"
 
 #include <cctype>
 
 #include "base/callback_helpers.h"
 #include "base/debug/trace_event.h"
@@ skipping 301 matching lines @@
     : test_interfaces_(NULL),
       delegate_(NULL),
       web_widget_(NULL),
       spellcheck_(new SpellCheckClient(this)),
       chooser_count_(0) {
   Reset();
 }
 
 WebTestProxyBase::~WebTestProxyBase() {
   test_interfaces_->windowClosed(this);
+  // Tests must wait for readback requests to finish before notifying that
+  // they are done.
+  CHECK_EQ(0u, composite_and_readback_callbacks_.size());
 }
 
 void WebTestProxyBase::SetInterfaces(WebTestInterfaces* interfaces) {
   test_interfaces_ = interfaces->testInterfaces();
   test_interfaces_->windowOpened(this);
 }
 
 void WebTestProxyBase::SetDelegate(WebTestDelegate* delegate) {
   delegate_ = delegate;
   spellcheck_->setDelegate(delegate);
@@ skipping 907 matching lines @@
   if (!push_client_.get())
     push_client_.reset(new MockWebPushClient);
   return push_client_.get();
 }
 
 blink::WebPushClient* WebTestProxyBase::GetWebPushClient() {
   return GetPushClientMock();
 }
 
 }  // namespace content