Reland of Adding task runner/ message loop to tests that use IsolateHolder.

gin/test/v8_test.h

Index: gin/test/v8_test.h
diff --git a/gin/test/v8_test.h b/gin/test/v8_test.h
index e9209ce97921fb17333382092b754b7ebc79970b..592b88904035a0160e7e87a1bb27fcaeb2310a97 100644
--- a/gin/test/v8_test.h
+++ b/gin/test/v8_test.h
@@ -8,6 +8,7 @@
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "base/memory/scoped_ptr.h"
+#include "base/message_loop/message_loop.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "v8/include/v8.h"
 
@@ -26,6 +27,7 @@ class V8Test : public testing::Test {
   void TearDown() override;
 
  protected:
+  base::MessageLoop message_loop_;
   scoped_ptr<IsolateHolder> instance_;
   v8::Persistent<v8::Context> context_;