[debugger] debug-evaluate should not not modify local values.

src/debug/debug-evaluate.cc

Index: src/debug/debug-evaluate.cc
diff --git a/src/debug/debug-evaluate.cc b/src/debug/debug-evaluate.cc
index 9d0d38446e0a6cd27ec9bca7e614544c4026b30b..b04952f2c573ed438f44e12ee48349f5516e2d59 100644
--- a/src/debug/debug-evaluate.cc
+++ b/src/debug/debug-evaluate.cc
@@ -77,7 +77,9 @@ MaybeHandle<Object> DebugEvaluate::Local(Isolate* isolate,
   MaybeHandle<Object> maybe_result = Evaluate(
       isolate, context_builder.outer_info(),
       context_builder.innermost_context(), context_extension, receiver, source);
-  if (!maybe_result.is_null()) context_builder.UpdateValues();
+  if (!maybe_result.is_null() && !FLAG_debug_eval_readonly_locals) {
+    context_builder.UpdateValues();
+  }
   return maybe_result;
 }
 
@@ -309,7 +311,7 @@ void DebugEvaluate::ContextBuilder::MaterializeArgumentsObject(
 
 
 MaybeHandle<Object> DebugEvaluate::ContextBuilder::LoadFromContext(
-    Handle<Context> context, Handle<String> name) {
+    Handle<Context> context, Handle<String> name, bool* global) {
   static const ContextLookupFlags flags = FOLLOW_CONTEXT_CHAIN;
   int index;
   PropertyAttributes attributes;
@@ -320,9 +322,13 @@ MaybeHandle<Object> DebugEvaluate::ContextBuilder::LoadFromContext(
   Handle<Object> value;
   if (index != Context::kNotFound) {  // Found on context.
     Handle<Context> context = Handle<Context>::cast(holder);
+    // Do not shadow variables on the script context.
+    *global = context->IsScriptContext();
     return Handle<Object>(context->get(index), isolate_);
   } else {  // Found on object.
     Handle<JSReceiver> object = Handle<JSReceiver>::cast(holder);
+    // Do not shadow properties on the global object.
+    *global = object->IsJSGlobalObject();
     return JSReceiver::GetDataProperty(object, name);
   }
 }
@@ -333,7 +339,13 @@ void DebugEvaluate::ContextBuilder::MaterializeContextChain(
   for (const Handle<String>& name : non_locals_) {
     HandleScope scope(isolate_);
     Handle<Object> value;
-    if (!LoadFromContext(context, name).ToHandle(&value)) continue;
+    bool global;
+    if (!LoadFromContext(context, name, &global).ToHandle(&value) || global) {
+      // If resolving the variable fails, skip it. If it resolves to a global
+      // variable, skip it as well since it's not read-only and can be resolved
+      // within debug-evaluate.
+      continue;
+    }
     JSObject::SetOwnPropertyIgnoreAttributes(target, name, value, NONE).Check();
   }
 }
@@ -381,7 +393,8 @@ Handle<Context> DebugEvaluate::ContextBuilder::MaterializeReceiver(
   Handle<Object> receiver = isolate_->factory()->undefined_value();
   Handle<String> this_string = isolate_->factory()->this_string();
   if (this_is_non_local) {
-    LoadFromContext(lookup_context, this_string).ToHandle(&receiver);
+    bool global;
+    LoadFromContext(lookup_context, this_string, &global).ToHandle(&receiver);
   } else if (local_function->shared()->scope_info()->HasReceiver()) {
     receiver = handle(frame_->receiver(), isolate_);
   }