[DevTools] use debug_frontend flag in content_shell for tests

content/shell/browser/layout_test/layout_test_devtools_frontend.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/browser/layout_test/layout_test_devtools_frontend.h"
 
 #include "base/command_line.h"
 #include "base/path_service.h"
 #include "base/strings/stringprintf.h"
 #include "build/build_config.h"
@@ skipping 35 matching lines @@
 #if defined(OS_MACOSX)
   // On Mac, the executable is in
   // out/Release/Content Shell.app/Contents/MacOS/Content Shell.
   // We need to go up 3 directories to get to out/Release.
   dir_exe = dir_exe.AppendASCII("../../..");
 #endif
   base::FilePath dev_tools_path =
       dir_exe.AppendASCII("resources/inspector/inspector.html");
 
   GURL result = net::FilePathToFileURL(dev_tools_path);
+  std::string url_string =
+      base::StringPrintf("%s?experiments=true", result.spec().c_str());
+#if defined(DEBUG_DEVTOOLS)
+  url_string += "&debugFrontend=true";
+#endif  // defined(DEBUG_DEVTOOLS)
   if (!settings.empty())
-    result = GURL(base::StringPrintf("%s?settings=%s&experiments=true",
-                                     result.spec().c_str(),
-                                     settings.c_str()));
-  return result;
+    url_string += "&settings=" + settings;
+  return GURL(url_string);
 }
 
 void LayoutTestDevToolsFrontend::ReuseFrontend(const std::string& settings,
                                                const std::string frontend_url) {
   DisconnectFromTarget();
   preferences()->Clear();
   frontend_shell()->LoadURL(GetDevToolsPathAsURL(settings, frontend_url));
 }
 
 LayoutTestDevToolsFrontend::LayoutTestDevToolsFrontend(
     Shell* frontend_shell,
     WebContents* inspected_contents)
     : ShellDevToolsFrontend(frontend_shell, inspected_contents) {
 }
 
 LayoutTestDevToolsFrontend::~LayoutTestDevToolsFrontend() {
 }
 
 void LayoutTestDevToolsFrontend::AgentHostClosed(
     DevToolsAgentHost* agent_host, bool replaced) {
   // Do not close the front-end shell.
 }
 
 void LayoutTestDevToolsFrontend::RenderProcessGone(
     base::TerminationStatus status) {
   BlinkTestController::Get()->DevToolsProcessCrashed();
 }
 
 }  // namespace content