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

gin/converter_unittest.cc

Index: gin/converter_unittest.cc
diff --git a/gin/converter_unittest.cc b/gin/converter_unittest.cc
index 940d4a224a37a137aa3ef6b6fd21e74a041e007a..8b9adf414b05899eb85830f90414e95ca74d216e 100644
--- a/gin/converter_unittest.cc
+++ b/gin/converter_unittest.cc
@@ -14,6 +14,8 @@
 #include "testing/gtest/include/gtest/gtest.h"
 #include "v8/include/v8.h"
 
+namespace gin {
+
 using v8::Array;
 using v8::Boolean;
 using v8::HandleScope;
@@ -26,8 +28,6 @@ using v8::String;
 using v8::Undefined;
 using v8::Value;
 
-namespace gin {
-
 typedef V8Test ConverterTest;
 
 TEST_F(ConverterTest, Bool) {