Reland: Use real revision mapping in bot_update module

scripts/slave/recipes/chromium.expected/full_chromium_chrome_Google_Chrome_Win.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "[BUILD]\\scripts\\slave\\kill_processes.py"
     ],
     "name": "taskkill"
   },
   {
     "abort_on_failure": true,
     "cmd": [
       "python",
       "-u",
       "[BUILD]\\scripts\\slave\\bot_update.py",
       "--master",
       "chromium.chrome",
       "--builder",
       "Google Chrome Win",
       "--slave",
       "TestSlavename",
       "--spec",
       "cache_dir = None\nsolutions = [{'custom_vars': {'googlecode_url': 'svn://svn-mirror.golo.chromium.org/%s', 'nacl_trunk': 'svn://svn-mirror.golo.chromium.org/native_client/trunk', 'sourceforge_url': 'svn://svn-mirror.golo.chromium.org/%(repo)s', 'webkit_trunk': 'svn://svn-mirror.golo.chromium.org/blink/trunk'}, 'deps_file': 'DEPS', 'managed': True, 'name': 'src', 'url': 'svn://svn-mirror.golo.chromium.org/chrome/trunk/src'}, {'custom_deps': {'src/chrome/test/data/firefox2_profile/searchplugins': None, 'src/chrome/test/data/firefox2_searchplugins': None, 'src/chrome/test/data/firefox3_profile/searchplugins': None, 'src/chrome/test/data/firefox3_searchplugins': None, 'src/chrome/test/data/osdd': None, 'src/chrome/test/data/perf/frame_rate/private': None, 'src/chrome/test/data/plugin': None, 'src/chrome/test/data/ssl/certs': None, 'src/data/autodiscovery': None, 'src/data/esctf': None, 'src/data/mach_ports': None, 'src/data/memory_test': None, 'src/data/mozilla_js_tests': None, 'src/data/page_cycler': None, 'src/data/selenium_core': None, 'src/data/tab_switching': None, 'src/tools/grit/grit/test/data': None, 'src/webkit/data/bmp_decoder': None, 'src/webkit/data/ico_decoder': None, 'src/webkit/data/test_shell/plugins': None, 'src/webkit/data/xbm_decoder': None}, 'deps_file': 'DEPS', 'managed': True, 'name': 'src-internal', 'url': 'svn://svn-mirror.golo.chromium.org/chrome-internal/trunk/src-internal'}]",
+      "--revision_mapping_file",
+      "{\"src\": \"got_revision\", \"src/native_client\": \"got_nacl_revision\", \"src/third_party/WebKit\": \"got_webkit_revision\", \"src/third_party/webrtc\": \"got_webrtc_revision\", \"src/tools/swarm_client\": \"got_swarm_client_revision\", \"src/tools/swarming_client\": \"got_swarming_client_revision\", \"src/v8\": \"got_v8_revision\"}",
       "--output_json",
       "/path/to/tmp/json"
     ],
     "name": "bot_update",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@json.output@{@@@",
       "@@@STEP_LOG_LINE@json.output@  \"did_run\": false@@@",
       "@@@STEP_LOG_LINE@json.output@}@@@",
       "@@@STEP_LOG_END@json.output@@@"
     ]
@@ skipping 133 matching lines @@
       "--json",
       "/path/to/tmp/json"
     ],
     "name": "checkdeps",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@json.output@[]@@@",
       "@@@STEP_LOG_END@json.output@@@"
     ]
   }
 ]