Harden yet more runtime functions

src/liveedit.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_LIVEEDIT_H_
 #define V8_LIVEEDIT_H_
 
 
 
 // Live Edit feature implementation.
@@ skipping 260 matching lines @@
   friend class JSArrayBasedStruct<FunctionInfoWrapper>;
 };
 
 
 // Wraps SharedFunctionInfo along with some of its fields for passing it
 // back to JavaScript. SharedFunctionInfo object itself is additionally
 // wrapped into BlindReference for sanitizing reasons.
 class SharedInfoWrapper : public JSArrayBasedStruct<SharedInfoWrapper> {
  public:
   static bool IsInstance(Handle<JSArray> array) {
-    return array->length() == Smi::FromInt(kSize_) &&
-        Object::GetElement(array->GetIsolate(), array, kSharedInfoOffset_)
-            .ToHandleChecked()->IsJSValue();
+    if (array->length() != Smi::FromInt(kSize_)) return false;
+    Handle<Object> element(
+        Object::GetElement(array->GetIsolate(),
+                           array,
+                           kSharedInfoOffset_).ToHandleChecked());
+    if (!element->IsJSValue()) return false;
+    return Handle<JSValue>::cast(element)->value()->IsSharedFunctionInfo();
   }
 
   explicit SharedInfoWrapper(Handle<JSArray> array)
       : JSArrayBasedStruct<SharedInfoWrapper>(array) {
   }
 
   void SetProperties(Handle<String> name,
                      int start_position,
                      int end_position,
                      Handle<SharedFunctionInfo> info);
 
   Handle<SharedFunctionInfo> GetInfo();
 
  private:
   static const int kFunctionNameOffset_ = 0;
   static const int kStartPositionOffset_ = 1;
   static const int kEndPositionOffset_ = 2;
   static const int kSharedInfoOffset_ = 3;
   static const int kSize_ = 4;
 
   friend class JSArrayBasedStruct<SharedInfoWrapper>;
 };
 
 } }  // namespace v8::internal
 
 #endif /* V*_LIVEEDIT_H_ */