Implement 'setVariableValue' for debugger block scopes.

test/mjsunit/harmony/debug-evaluate-blockscopes.js

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 49 matching lines @@
 // Add the debug event listener.
 Debug.setListener(listener);
 result = -1;
 f();
 assertEquals(1, result);
 
 // Clear breakpoint.
 Debug.clearBreakPoint(bp);
 // Get rid of the debug event listener.
 Debug.setListener(null);
+
+
+function f1() {
+  {
+    let i = 1;
+    debugger;
+    assertEquals(2, i);
+  }
+}
+
+function f2() {
+  {
+    let i = 1;
+    debugger;
+    assertEquals(2, i);
+    return function() { return i++; }
+  }
+}
+
+var exception;
+Debug.setListener(function (event, exec_state, event_data, data) {
+  try {
+    if (event == Debug.DebugEvent.Break) {
+      var frame = exec_state.frame();
+      assertEquals(1, frame.evaluate("i").value());
+      var allScopes = frame.allScopes();
+      assertEquals(1, allScopes[0].scopeObject().value().i);
+      allScopes[0].setVariableValue("i", 2);
+    }
+  } catch (e) {
+    exception = e;
+  }
+});
+
+exception = null;
+f1();
+assertEquals(null, exception, exception);
+exception = null;
+f2();
+assertEquals(null, exception, exception);