Allow Waitable event to be used to intentionally hang the UI thread for debugging purposes.

content/browser/frame_host/debug_urls.cc

 // 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/browser/frame_host/debug_urls.h"
 
 #if defined(SYZYASAN)
 #include <windows.h>
 #endif
 
 #include <vector>
 
 #include "base/command_line.h"
 #include "base/debug/asan_invalid_access.h"
 #include "base/debug/profiler.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/synchronization/waitable_event.h"
+#include "base/threading/thread_restrictions.h"
 #include "cc/base/switches.h"
 #include "content/browser/gpu/gpu_process_host_ui_shim.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/common/content_constants.h"
 #include "content/public/common/url_constants.h"
 #include "ppapi/proxy/ppapi_messages.h"
 #include "url/gurl.h"
 
 #if defined(ENABLE_PLUGINS)
 #include "content/browser/ppapi_plugin_process_host.h"
@@ skipping 115 matching lines @@
     return false;
   }
 #endif
 
   return true;
 }
 
 
 }  // namespace
 
+class ScopedAllowWaitForDebugURL {
+ private:
+  base::ThreadRestrictions::ScopedAllowWait wait;
+};
+
 bool HandleDebugURL(const GURL& url, ui::PageTransition transition) {
   // Ensure that the user explicitly navigated to this URL, unless
   // kEnableGpuBenchmarking is enabled by Telemetry.
   bool is_telemetry_navigation =
       base::CommandLine::ForCurrentProcess()->HasSwitch(
           cc::switches::kEnableGpuBenchmarking) &&
       (transition & ui::PAGE_TRANSITION_TYPED);
 
   if (!(transition & ui::PAGE_TRANSITION_FROM_ADDRESS_BAR) &&
       !is_telemetry_navigation)
     return false;
 
   if (IsAsanDebugURL(url))
     return HandleAsanDebugURL(url);
 
   if (IsKaskoDebugURL(url)) {
     HandleKaskoDebugURL();
     return true;
   }
 
   if (url == GURL(kChromeUIBrowserCrashURL)) {
     // Induce an intentional crash in the browser process.
     CHECK(false);
     return true;
   }
 
   if (url == GURL(kChromeUIBrowserUIHang)) {
+    ScopedAllowWaitForDebugURL allow_wait;
     base::WaitableEvent(false, false).Wait();
     return true;
   }
 
   if (url == GURL(kChromeUIGpuCleanURL)) {
     GpuProcessHostUIShim* shim = GpuProcessHostUIShim::GetOneInstance();
     if (shim)
       shim->SimulateRemoveAllContext();
     return true;
   }
@@ skipping 30 matching lines @@
     return true;
 
   return url == GURL(kChromeUICrashURL) ||
          url == GURL(kChromeUIDumpURL) ||
          url == GURL(kChromeUIKillURL) ||
          url == GURL(kChromeUIHangURL) ||
          url == GURL(kChromeUIShorthangURL);
 }
 
 }  // namespace content