Make it possible to Crankshaft all kinds of stubs.

src/compiler.h

Index: src/compiler.h
diff --git a/src/compiler.h b/src/compiler.h
index 5e69661b4d8b92d1ad9c986ef49a129d7deebf42..dae39db351bc0ee9db4d8a3ecb3dcf80ceeff9a2 100644
--- a/src/compiler.h
+++ b/src/compiler.h
@@ -79,7 +79,7 @@ class CompilationInfo {
   Handle<JSFunction> closure() const { return closure_; }
   Handle<SharedFunctionInfo> shared_info() const { return shared_info_; }
   Handle<Script> script() const { return script_; }
-  HydrogenCodeStub* code_stub() {return code_stub_; }
+  HydrogenCodeStub* code_stub() const {return code_stub_; }
   v8::Extension* extension() const { return extension_; }
   ScriptDataImpl* pre_parse_data() const { return pre_parse_data_; }
   Handle<Context> context() const { return context_; }