[debugger] correctly find inner function scope.

test/inspector/debugger/step-into-nested-arrow.js

+// Copyright 2017 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.
+
+InspectorTest.log(
+    'Checks that stepInto nested arrow function doesn\'t produce crash.');
+
+InspectorTest.setupScriptMap();
+InspectorTest.addScript(`
+const rec = (x) => (y) =>
+rec();
+//# sourceURL=test.js`);
+
+Protocol.Debugger.onPaused(message => {
+  InspectorTest.log("paused");
+  InspectorTest.logCallFrames(message.params.callFrames);
+  Protocol.Debugger.stepInto();
+})
+
+Protocol.Debugger.enable();
+Protocol.Debugger.setBreakpointByUrl({ url: 'test.js', lineNumber: 2 })
+  .then(() => Protocol.Runtime.evaluate({ expression: 'rec(5)(4)' }))
+  .then(InspectorTest.completeTest);