Ensure that privates are private.

extensions/renderer/utils_native_handler.cc

Index: extensions/renderer/utils_native_handler.cc
diff --git a/extensions/renderer/utils_native_handler.cc b/extensions/renderer/utils_native_handler.cc
index 1ded40c6ad2b0017c86c761782c33c6b8311d086..66fc458e4e068afa50d69d2502c07efd817170f8 100644
--- a/extensions/renderer/utils_native_handler.cc
+++ b/extensions/renderer/utils_native_handler.cc
@@ -4,13 +4,29 @@
 
 #include "extensions/renderer/utils_native_handler.h"
 
+#include <algorithm>
+
 #include "base/macros.h"
+#include "base/strings/string_util.h"
 #include "base/strings/stringprintf.h"
 #include "extensions/renderer/script_context.h"
 #include "third_party/WebKit/public/web/WebSerializedScriptValue.h"
 
 namespace extensions {
 
+namespace {
+
+// Returns whether |name| can safely be used as an identifier in JavaScript code
+// without side effects. This method allows syntax errors, but not execution of
+// arbitrary JavaScript code.
+bool IsAllowedFunctionName(const std::string& name) {
+  return std::find_if_not(name.begin(), name.end(), [](char c) {
+           return base::IsAsciiAlpha(c);
+         }) == name.end();
+}
+
+}  // namespace
+
 UtilsNativeHandler::UtilsNativeHandler(ScriptContext* context)
     : ObjectBackedNativeHandler(context) {
   RouteFunction("createClassWrapper",
@@ -28,6 +44,7 @@ void UtilsNativeHandler::CreateClassWrapper(
   CHECK_EQ(3, args.Length());
   CHECK(args[0]->IsString());
   std::string name = *v8::String::Utf8Value(args[0]);
+  CHECK(IsAllowedFunctionName(name));
   CHECK(args[1]->IsObject());
   v8::Local<v8::Object> cls = args[1].As<v8::Object>();
   CHECK(args[2]->IsObject() || args[2]->IsUndefined());