[debugger] account for inlined functions when stepping.

test/debugger/regress/regress-5901-2.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.
+
+function f() {
+  debugger;
+  return 1;
+}
+
+function g() {
+  return f();
+}  // Break
+
+function h() {
+  return g();
+}
+
+h();
+h();
+
+var Debug = debug.Debug;
+var step_count = 0;
+var exception = null;
+
+function listener(event, exec_state, event_data, data) {
+  if (event != Debug.DebugEvent.Break) return;
+  try {
+    if (step_count == 0) {
+      exec_state.prepareStep(Debug.StepAction.StepOut);
+    } else {
+      assertTrue(exec_state.frame().sourceLineText().includes('Break'));
+    }
+    step_count++;
+  } catch (e) {
+    exception = e;
+    print(e);
+  }
+}
+
+Debug.setListener(listener);
+% OptimizeFunctionOnNextCall(h);
+h();
+Debug.setListener(null);
+assertNull(exception);
+assertEquals(2, step_count);