setup the correct version of Xcode

scripts/slave/recipes/flutter/flutter.expected/mac_cannot_find_xcode.json

+[
+  {
+    "cmd": [
+      "python",
+      "-u",
+      "\nimport os, sys\nfrom common import chromium_utils # Error? See https://crbug.com/584783.\n\npath = sys.argv[1]\nif os.path.exists(path):\n  for p in (os.path.join(path, x) for x in os.listdir(path)):\n    if os.path.isdir(p):\n      chromium_utils.RemoveDirectory(p)\n    else:\n      os.unlink(p)\n",
+      "[SLAVE_BUILD]"
+    ],
+    "cwd": "[SLAVE_BUILD]",
+    "name": "rmcontents everything",
+    "~followup_annotations": [
+      "@@@STEP_LOG_LINE@python.inline@@@@",
+      "@@@STEP_LOG_LINE@python.inline@import os, sys@@@",
+      "@@@STEP_LOG_LINE@python.inline@from common import chromium_utils # Error? See https://crbug.com/584783.@@@",
+      "@@@STEP_LOG_LINE@python.inline@@@@",
+      "@@@STEP_LOG_LINE@python.inline@path = sys.argv[1]@@@",
+      "@@@STEP_LOG_LINE@python.inline@if os.path.exists(path):@@@",
+      "@@@STEP_LOG_LINE@python.inline@  for p in (os.path.join(path, x) for x in os.listdir(path)):@@@",
+      "@@@STEP_LOG_LINE@python.inline@    if os.path.isdir(p):@@@",
+      "@@@STEP_LOG_LINE@python.inline@      chromium_utils.RemoveDirectory(p)@@@",
+      "@@@STEP_LOG_LINE@python.inline@    else:@@@",
+      "@@@STEP_LOG_LINE@python.inline@      os.unlink(p)@@@",
+      "@@@STEP_LOG_END@python.inline@@@"
+    ]
+  },
+  {
+    "cmd": [
+      "python",
+      "-u",
+      "RECIPE_MODULE[depot_tools::git]/resources/git_setup.py",
+      "--path",
+      "[SLAVE_BUILD]/flutter",
+      "--url",
+      "https://chromium.googlesource.com/external/github.com/flutter/flutter"
+    ],
+    "cwd": "[SLAVE_BUILD]",
+    "name": "git setup"
+  },
+  {
+    "cmd": [
+      "git",
+      "retry",
+      "fetch",
+      "origin",
+      "master",
+      "--recurse-submodules"
+    ],
+    "cwd": "[SLAVE_BUILD]/flutter",
+    "name": "git fetch"
+  },
+  {
+    "cmd": [
+      "git",
+      "checkout",
+      "-f",
+      "FETCH_HEAD"
+    ],
+    "cwd": "[SLAVE_BUILD]/flutter",
+    "name": "git checkout"
+  },
+  {
+    "cmd": [
+      "git",
+      "rev-parse",
+      "HEAD"
+    ],
+    "cwd": "[SLAVE_BUILD]/flutter",
+    "name": "read revision",
+    "stdout": "/path/to/tmp/",
+    "~followup_annotations": [
+      "@@@STEP_TEXT@<br/>checked out 'deadbeef'<br/>@@@",
+      "@@@SET_BUILD_PROPERTY@got_revision@\"deadbeef\"@@@"
+    ]
+  },
+  {
+    "cmd": [
+      "git",
+      "clean",
+      "-f",
+      "-d",
+      "-x"
+    ],
+    "cwd": "[SLAVE_BUILD]/flutter",
+    "name": "git clean"
+  },
+  {
+    "cmd": [
+      "git",
+      "submodule",
+      "sync"
+    ],
+    "cwd": "[SLAVE_BUILD]/flutter",
+    "name": "submodule sync"
+  },
+  {
+    "cmd": [
+      "git",
+      "submodule",
+      "update",
+      "--init",
+      "--recursive"
+    ],
+    "cwd": "[SLAVE_BUILD]/flutter",
+    "name": "submodule update"
+  },
+  {
+    "cmd": [
+      "[SLAVE_BUILD]/flutter/infra/download_android_tools.py"
+    ],
+    "cwd": "[SLAVE_BUILD]",
+    "name": "download android tools"
+  },
+  {
+    "cmd": [
+      "python",
+      "-u",
+      "[BUILD]/scripts/slave/ios/find_xcode.py",
+      "--json-file",
+      "/path/to/tmp/json"
+    ],
+    "cwd": "[SLAVE_BUILD]",
+    "env": {
+      "ANDROID_HOME": "[SLAVE_BUILD]/flutter/infra/android_tools",
+      "PATH": "[SLAVE_BUILD]/flutter/bin:[SLAVE_BUILD]/flutter/bin/cache/dart-sdk/bin:%(PATH)s",
+      "PUB_CACHE": "[SLAVE_BUILD]/.pub-cache"
+    },
+    "name": "enumerate_xcode_installations",
+    "~followup_annotations": [
+      "@@@STEP_LOG_LINE@json.output@{@@@",
+      "@@@STEP_LOG_LINE@json.output@  \"installations\": {}@@@",
+      "@@@STEP_LOG_LINE@json.output@}@@@",
+      "@@@STEP_LOG_END@json.output@@@"
+    ]
+  },
+  {
+    "name": "$result",
+    "reason": "Xcode version 7 or above not found",
+    "status_code": 1
+  }
+]