[debugger] add test case for stepping into proxy traps.

R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/1508653002

Cr-Commit-Position: refs/heads/master@{#32671}

test/mjsunit/harmony/debug-stepin-proxies.js

+// Copyright 2015 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 --harmony-proxies
+
+Debug = debug.Debug
+
+var exception = null;
+var log = [];
+
+function listener(event, exec_state, event_data, data) {
+  if (event != Debug.DebugEvent.Break) return;
+  try {
+    print(event_data.sourceLineText());
+    var entry = "";
+    for (var i = 0; i < exec_state.frameCount(); i++) {
+      entry += exec_state.frame(i).sourceLineText().substr(-1);
+      entry += exec_state.frame(i).sourceColumn();
+    }
+    log.push(entry);
+    exec_state.prepareStep(Debug.StepAction.StepIn, 1);
+  } catch (e) {
+    exception = e;
+  }
+};
+
+var target = {};
+var handler = {
+  has: function(target, name) {
+    return true;                     // h
+  },                                 // i
+  get: function(target, name) {
+    return 42;                       // j
+  },                                 // k
+  set: function(target, name, value) {
+    return false;                    // l
+  },                                 // m
+  enumerate: function(target) {
+    function* keys() {               // n
+      yield "foo";                   // o
+      yield "bar";                   // p
+    }                                // q
+    return keys();                   // r
+  },                                 // s
+}
+
+var proxy = new Proxy(target, handler);
+
+Debug.setListener(listener);
+debugger;                            // a
+var has = "step" in proxy;           // b
+var get = proxy.step;                // c
+proxy.step = 43;                     // d
+for (var i in proxy) {               // e
+  log.push(i);                       // f
+}
+
+Debug.setListener(null);             // g
+
+assertNull(exception);
+assertTrue(has);
+assertEquals(42, get);
+
+assertEquals([
+  "a0",
+  "b0", "h4b20", "i2b20",                           // [[Has]]
+  "c0", "j4c15", "k2c15",                           // [[Get]]
+  "d0", "l4d11", "m2d11",                           // [[Set]]
+  "e14", "r4e14", "q4r11e14", "s2e14",              // for-in [[Enumerate]]
+      "o6e14", "q4e14", "p6e14", "q4e14", "q4e14",  // exhaust iterator
+  "e9","f2","foo","e9","f2", "bar","e9",            // for-in body
+  "g0"
+], log);