Minor improvements to reftests.

sky/tools/tester/test_runner.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 "sky/tools/tester/test_runner.h"
 
 #include <iostream>
 #include "base/bind.h"
 #include "mojo/public/cpp/application/connect.h"
 #include "mojo/public/cpp/application/service_provider_impl.h"
@@ skipping 37 matching lines @@
   std::cout << "Content-Type: text/plain\n";
   std::cout << test_result << "\n";
   std::cout << "#EOF\n";
 
   // TODO(ojan): Don't generate the pixels if enable_pixel_dumping_ is false.
   if (enable_pixel_dumping_) {
     // TODO(ojan): Add real hashes here once we want to do pixel tests.
     std::cout << "\nActualHash: FAKEHASHSTUB\n";
     std::cout << "Content-Type: image/png\n";
     std::cout << "Content-Length: " << pixels.size() << "\n";
+    CHECK(pixels.size()) << "Could not dump pixels. Did you call notifyTestComplete before the first paint?";
     std::cout.write(
         reinterpret_cast<const char*>(&pixels[0]), pixels.size());
   }
 
   std::cout << "#EOF\n";
   std::cout.flush();
   std::cerr << "#EOF\n";
   std::cerr.flush();
 
   client_->OnTestComplete();
 }
 
 }  // namespace tester
 }  // namespace sky