[debugger] fix debug-evaluate wrt shadowed context var.

test/mjsunit/es6/debug-evaluate-arrow-function-receiver.js

+// Copyright 2015 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.
+
+// Flags: --expose-debug-as debug
+
+// Test that debug-evaluate can find the correct this value for an
+// arrow function.
+
+Debug = debug.Debug
+
+var break_count = 0;
+var exception = null;
+
+function listener(event, exec_state, event_data, data) {
+  if (event != Debug.DebugEvent.Break) return;
+  try {
+    for (var i = 0; i < exec_state.frameCount() - 1; i++) {
+      var frame = exec_state.frame(0);
+      var this_value = frame.evaluate("this").value();
+      if (frame.sourceLineText().indexOf("undefined this") > 0) {
+        assertEquals(undefined, this_value);
+      } else {
+        assertEquals(receiver, this_value);
+      }
+    }
+    break_count++;
+  } catch (e) {
+    exception = e;
+  }
+}
+
+var receiver = {};
+
+// Context-allocated receiver.
+function f() {
+  assertEquals(receiver, this);
+  debugger;
+  return () => {
+    assertEquals(receiver, this);
+    debugger;
+    with ({}) {
+      return () => {
+        debugger;
+        try {
+          throw new Error();
+        } catch (e) {
+          return () => {
+            debugger;
+            return g.call(receiver);
+          };
+        }
+      };
+    }
+  };
+}
+
+// Stack-allocated receiver.
+function g() {
+  debugger;
+  return () => {
+    debugger;  // undefined this.
+    with ({}) {
+      return () => {
+        debugger;  // undefined this.
+        try {
+          throw new Error();
+        } catch (e) {
+          return () => {
+            debugger;  // undefined this.
+            return f.call(receiver);
+          };
+        }
+      };
+    }
+  };
+}
+
+Debug.setListener(listener);
+
+var h = f.call(receiver);
+for (var i = 0; i < 20; i++) h = h();
+var h = g.call(receiver);
+for (var i = 0; i < 20; i++) h = h();
+
+Debug.setListener(null);
+
+assertEquals(54, break_count);
+assertNull(exception);