[DevTools] Use InspectorFrontendHost.readyForTest for layout tests.

chrome/browser/devtools/devtools_window_testing.cc

Index: chrome/browser/devtools/devtools_window_testing.cc
diff --git a/chrome/browser/devtools/devtools_window_testing.cc b/chrome/browser/devtools/devtools_window_testing.cc
index f87939d3723f7b7d9825ac61766cb43df08311b6..6782d31c6781cbf1f8c1bde69a187d654327a0da 100644
--- a/chrome/browser/devtools/devtools_window_testing.cc
+++ b/chrome/browser/devtools/devtools_window_testing.cc
@@ -96,10 +96,12 @@ void DevToolsWindowTesting::WindowClosed(DevToolsWindow* window) {
 
 // static
 void DevToolsWindowTesting::WaitForDevToolsWindowLoad(DevToolsWindow* window) {
-  scoped_refptr<content::MessageLoopRunner> runner =
-      new content::MessageLoopRunner;
-  window->ready_for_test_callback_ = runner->QuitClosure();
-  runner->Run();
+  if (!window->ready_for_test_) {
+    scoped_refptr<content::MessageLoopRunner> runner =
+        new content::MessageLoopRunner;
+    window->ready_for_test_callback_ = runner->QuitClosure();
+    runner->Run();
+  }
   base::string16 harness = base::UTF8ToUTF16(
       content::DevToolsFrontendHost::GetFrontendResource(kHarnessScript));
   window->main_web_contents_->GetMainFrame()->ExecuteJavaScript(harness);