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

test/mjsunit/debug-evaluate-locals.js

 // Copyright 2008 the V8 project authors. All rights reserved.
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-// Flags: --expose-debug-as debug --debug-eval-readonly-locals
+// Flags: --expose-debug-as debug
 // Get the Debug object exposed from the debug context global object.
 Debug = debug.Debug
 
 listenerComplete = false;
 exception = false;
 
 
 function h() {
   var a = 1;
   var b = 2;
@@ skipping 67 matching lines @@
 
 
 function listener(event, exec_state, event_data, data) {
   try {
     if (event == Debug.DebugEvent.Break)
     {
       checkFrame0(exec_state.frame(0));
       checkFrame1(exec_state.frame(1));
       checkFrame2(exec_state.frame(2));
 
-      // Evaluating a and b on frames 0, 1 and 2 produces 1, 2, 3, 4, 5 and 6.
       assertEquals(1, exec_state.frame(0).evaluate('a').value());
       assertEquals(2, exec_state.frame(0).evaluate('b').value());
       assertEquals(5, exec_state.frame(0).evaluate('eval').value());
       assertEquals(3, exec_state.frame(1).evaluate('a').value());
-      // Reference error because g does not reference b.
-      assertThrows(() => exec_state.frame(1).evaluate('b'), ReferenceError);
+      assertEquals(4, exec_state.frame(1).evaluate('b').value());
       assertEquals("function",
                    typeof exec_state.frame(1).evaluate('eval').value());
       assertEquals(5, exec_state.frame(2).evaluate('a').value());
       assertEquals(6, exec_state.frame(2).evaluate('b').value());
       assertEquals("function",
                    typeof exec_state.frame(2).evaluate('eval').value());
-      // Assignments to local variables only have temporary effect.
       assertEquals("foo",
                    exec_state.frame(0).evaluate('a = "foo"').value());
       assertEquals("bar",
                    exec_state.frame(1).evaluate('a = "bar"').value());
       // Indicate that all was processed.
       listenerComplete = true;
     }
   } catch (e) {
     exception = e;
     print("Caught something. " + e + " " + e.stack);
   };
 };
 
 // Add the debug event listener.
 Debug.setListener(listener);
 
 var f_result = f();
 
-assertEquals(4, f_result);
+assertEquals("foobar", f_result);
 
 // Make sure that the debug event listener was invoked.
 assertFalse(exception, "exception in listener")
 assertTrue(listenerComplete);