content_shell: Use a ThreadRestrictions::ScopedAllowWait for layout tests on Android.

content/shell/webkit_test_controller.h

Index: content/shell/webkit_test_controller.h
diff --git a/content/shell/webkit_test_controller.h b/content/shell/webkit_test_controller.h
index b451aba0556786c5d2c5c7bd843976fa5ff94e40..380f5e0add97faecb0a37220aeee497bf49b38b9 100644
--- a/content/shell/webkit_test_controller.h
+++ b/content/shell/webkit_test_controller.h
@@ -20,12 +20,27 @@
 #include "ui/gfx/size.h"
 #include "webkit/common/webpreferences.h"
 
+#if defined(OS_ANDROID)
+#include "base/threading/thread_restrictions.h"
+#endif
+
 class SkBitmap;
 
 namespace content {
 
 class Shell;
 
+#if defined(OS_ANDROID)
+// Android uses a nested message loop for running layout tests because the
+// default message loop, provided by the system, does not offer a blocking
+// Run() method. The loop itself, implemented as NestedMessagePumpAndroid,
+// uses a base::WaitableEvent allowing it to sleep until more events arrive.
+class ScopedAllowWaitForAndroidLayoutTests {
+ private:
+  base::ThreadRestrictions::ScopedAllowWait wait;
+};
+#endif
+
 class WebKitTestResultPrinter {
  public:
   WebKitTestResultPrinter(std::ostream* output, std::ostream* error);
@@ -189,6 +204,12 @@ class WebKitTestController : public base::NonThreadSafe,
 
   NotificationRegistrar registrar_;
 
+#if defined(OS_ANDROID)
+  // Because of the nested message pump implementation, Android needs to allow
+  // waiting on the UI thread while layout tests are being ran.
+  ScopedAllowWaitForAndroidLayoutTests reduced_restrictions_;
+#endif
+
   DISALLOW_COPY_AND_ASSIGN(WebKitTestController);
 };