[debugger] allow debug-evaluate to change stack and context values.

src/contexts.cc

Index: src/contexts.cc
diff --git a/src/contexts.cc b/src/contexts.cc
index 9adccb2897778611d6a89556561218371791175e..67a9fea8b896d2be7115b7fb56ad724cc02c4e0b 100644
--- a/src/contexts.cc
+++ b/src/contexts.cc
@@ -233,6 +233,7 @@ Handle<Object> Context::Lookup(Handle<String> name,
   Handle<Context> context(this, isolate);
 
   bool follow_context_chain = (flags & FOLLOW_CONTEXT_CHAIN) != 0;
+  bool failed_whitelist = false;
   *index = kNotFound;
   *attributes = ABSENT;
   *binding_flags = MISSING_BINDING;
@@ -378,6 +379,31 @@ Handle<Object> Context::Lookup(Handle<String> name,
         *binding_flags = MUTABLE_IS_INITIALIZED;
         return context;
       }
+    } else if (context->IsDebugEvaluateContext()) {
+      // Check materialized locals.
+      Object* obj = context->get(EXTENSION_INDEX);
+      if (obj->IsJSReceiver()) {
+        Handle<JSReceiver> extension(JSReceiver::cast(obj));
+        LookupIterator it(extension, name, extension);
+        Maybe<bool> found = JSReceiver::HasProperty(&it);
+        if (found.FromMaybe(false)) {
+          *attributes = NONE;
+          return extension;
+        }
+      }
+      // Check the original context, but do not follow its context chain.
+      obj = context->get(WRAPPED_CONTEXT_INDEX);
+      if (obj->IsContext()) {
+        Handle<Object> result = Context::cast(obj)->Lookup(
+            name, DONT_FOLLOW_CHAINS, index, attributes, binding_flags);
+        if (!result.is_null()) return result;
+      }
+      // Check whitelist. Names that do not pass whitelist shall only resolve
+      // to with, script or native contexts up the context chain.
+      obj = context->get(WHITE_LIST_INDEX);
+      if (obj->IsStringSet()) {
+        failed_whitelist = failed_whitelist || !StringSet::cast(obj)->Has(name);
+      }
     }
 
     // 3. Prepare to continue with the previous (next outermost) context.
@@ -386,7 +412,12 @@ Handle<Object> Context::Lookup(Handle<String> name,
          context->is_declaration_context())) {
       follow_context_chain = false;
     } else {
-      context = Handle<Context>(context->previous(), isolate);
+      do {
+        context = Handle<Context>(context->previous(), isolate);
+        // If we come across a whitelist context, and the name is not
+        // whitelisted, then only consider with, script or native contexts.
+      } while (failed_whitelist && !context->IsScriptContext() &&
+               !context->IsNativeContext() && !context->IsWithContext());
     }
   } while (follow_context_chain);