depot_tools: add infra_paths recipe module for infra-specific paths

recipe_modules/gclient/example.expected/basic.json

Index: recipe_modules/gclient/example.expected/basic.json
diff --git a/recipe_modules/gclient/example.expected/basic.json b/recipe_modules/gclient/example.expected/basic.json
index e1ce307c9da57ace9a9ac17929f03c98d48140d8..3d2ba3213f4478ae2d1e55c88c6bb1736641ab33 100644
--- a/recipe_modules/gclient/example.expected/basic.json
+++ b/recipe_modules/gclient/example.expected/basic.json
@@ -8,7 +8,6 @@
       "--spec",
       "cache_dir = '[ROOT]/git_cache'\nsolutions = [{'deps_file': '.DEPS.git', 'managed': True, 'name': 'src', 'url': 'https://chromium.googlesource.com/chromium/src.git'}]"
     ],
-    "cwd": "[SLAVE_BUILD]",
     "env": {
       "PATH": "%(PATH)s:RECIPE_PACKAGE_REPO[depot_tools]"
     },
@@ -32,7 +31,6 @@
       "--output-json",
       "/path/to/tmp/json"
     ],
-    "cwd": "[SLAVE_BUILD]",
     "env": {
       "PATH": "%(PATH)s:RECIPE_PACKAGE_REPO[depot_tools]"
     },
@@ -59,7 +57,6 @@
       "user.name",
       "local_bot"
     ],
-    "cwd": "[SLAVE_BUILD]",
     "env": {
       "PATH": "%(PATH)s:RECIPE_PACKAGE_REPO[depot_tools]"
     },
@@ -76,7 +73,6 @@
       "user.email",
       "local_bot@example.com"
     ],
-    "cwd": "[SLAVE_BUILD]",
     "env": {
       "PATH": "%(PATH)s:RECIPE_PACKAGE_REPO[depot_tools]"
     },
@@ -89,9 +85,9 @@
       "RECIPE_PACKAGE_REPO[depot_tools]/gclient.py",
       "config",
       "--spec",
-      "cache_dir = '[GIT_CACHE]'\nsolutions = [{'deps_file': 'DEPS', 'managed': True, 'name': 'WebKit', 'safesync_url': 'https://blink-status.appspot.com/lkgr', 'url': 'svn://svn.chromium.org/blink/trunk'}]"
+      "cache_dir = '[ROOT]/b/build/slave/cache_dir'\nsolutions = [{'deps_file': 'DEPS', 'managed': True, 'name': 'WebKit', 'safesync_url': 'https://blink-status.appspot.com/lkgr', 'url': 'svn://svn.chromium.org/blink/trunk'}]"
     ],
-    "cwd": "[SLAVE_BUILD]/src/third_party",
+    "cwd": "[CWD]/src/third_party",
     "env": {
       "PATH": "%(PATH)s:RECIPE_PACKAGE_REPO[depot_tools]"
     },
@@ -113,7 +109,7 @@
       "--output-json",
       "/path/to/tmp/json"
     ],
-    "cwd": "[SLAVE_BUILD]/src/third_party",
+    "cwd": "[CWD]/src/third_party",
     "env": {
       "PATH": "%(PATH)s:RECIPE_PACKAGE_REPO[depot_tools]"
     },
@@ -138,9 +134,8 @@
       "python",
       "-u",
       "\nimport os, sys\n\nbuild_path = sys.argv[1]\nif os.path.exists(build_path):\n  for (path, dir, files) in os.walk(build_path):\n    for cur_file in files:\n      if cur_file.endswith('index.lock'):\n        path_to_file = os.path.join(path, cur_file)\n        print 'deleting %s' % path_to_file\n        os.remove(path_to_file)\n",
-      "[SLAVE_BUILD]"
+      "[CWD]"
     ],
-    "cwd": "[SLAVE_BUILD]",
     "name": "cleanup index.lock",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@python.inline@@@@",
@@ -164,7 +159,6 @@
       "RECIPE_PACKAGE_REPO[depot_tools]/gclient.py",
       "runhooks"
     ],
-    "cwd": "[SLAVE_BUILD]",
     "env": {
       "PATH": "%(PATH)s:RECIPE_PACKAGE_REPO[depot_tools]"
     },