[debugger] keep scope and context chain for hidden scopes in sync.

test/mjsunit/regress/regress-crbug-609046.js

 // Copyright 2016 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 hidden scopes are correctly walked in the scope chain.
+
 var Debug = debug.Debug;
 var exception = null;
+var delegate = null;
+var done = false;
 
 function listener(event, exec_state, event_data, data) {
   if (event != Debug.DebugEvent.Break) return;
   try {
-    assertThrows(() => exec_state.frame(0).evaluate("bar.baz"), ReferenceError);
+    assertEquals([ debug.ScopeType.Block,
+                   debug.ScopeType.Script,
+                   debug.ScopeType.Global ],
+                 exec_state.frame(0).allScopes().map(s => s.scopeType()));
+    done = true;
   } catch (e) {
     exception = e;
   }
 }
 
 Debug.setListener(listener);
 
-(function() {
-  debugger;    // bar is still in TDZ at this point.
-  let bar = 1;
-  (x => bar);  // force bar to be context-allocated.
-})();
+for(let a = 0; a < 3; a++) {
+  debugger;
+  eval();  // Force context-allocation of everything.
+}
 
 Debug.setListener(null);
 assertNull(exception);
+assertTrue(done);