Make MSVC happy again.

TBR=bmeurer@chromium.org

Review URL: https://codereview.chromium.org/371813003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22234 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/hydrogen-instructions.h

@@ -23,7 +23,7 @@ namespace v8 {
 namespace internal {
 
 // Forward declarations.
-class ChangesOf;
+struct ChangesOf;
 class HBasicBlock;
 class HDiv;
 class HEnvironment;