Add support for "additional_mirrors" property in trybot configs.

scripts/slave/recipes/chromium_trybot.expected/analyze_finds_invalid_target.json

Index: scripts/slave/recipes/chromium_trybot.expected/analyze_finds_invalid_target.json
diff --git a/scripts/slave/recipes/chromium_trybot.expected/analyze_finds_invalid_target.json b/scripts/slave/recipes/chromium_trybot.expected/analyze_finds_invalid_target.json
index 3433180501865fff727e533851e7ecc23e20dc8d..4b6c6cf9b27ac7983fe242f1a6e410bdc95b66b3 100644
--- a/scripts/slave/recipes/chromium_trybot.expected/analyze_finds_invalid_target.json
+++ b/scripts/slave/recipes/chromium_trybot.expected/analyze_finds_invalid_target.json
@@ -11,7 +11,7 @@
       "--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'}]",
+      "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'}]",
       "--root",
       "src",
       "--revision_mapping_file",
@@ -118,7 +118,7 @@
     "cwd": "[SLAVE_BUILD]",
     "env": {
       "GYP_CHROMIUM_NO_ACTION": "1",
-      "GYP_DEFINES": "archive_gpu_tests=1 component=static_library dcheck_always_on=1 fastbuild=1 ffmpeg_branding=Chrome gomadir='[BUILD]/goma' proprietary_codecs=1 target_arch=x64 test_isolation_mode=prepare use_goma=1"
+      "GYP_DEFINES": "archive_gpu_tests=1 component=static_library dcheck_always_on=1 fastbuild=1 ffmpeg_branding=Chrome gomadir='[BUILD]/goma' internal_gles2_conform_tests=1 proprietary_codecs=1 target_arch=x64 test_isolation_mode=prepare use_goma=1"
     },
     "name": "gclient runhooks (with patch)"
   },
@@ -148,6 +148,22 @@
     "cmd": [
       "python",
       "-u",
+      "\nimport shutil\nimport sys\nshutil.copy(sys.argv[1], sys.argv[2])\n",
+      "[SLAVE_BUILD]/src/testing/buildbot/chromium.gpu.json",
+      "/path/to/tmp/json"
+    ],
+    "cwd": "[SLAVE_BUILD]",
+    "name": "read test spec (2)",
+    "~followup_annotations": [
+      "@@@STEP_TEXT@path: [SLAVE_BUILD]/src/testing/buildbot/chromium.gpu.json@@@",
+      "@@@STEP_LOG_LINE@json.output@{}@@@",
+      "@@@STEP_LOG_END@json.output@@@"
+    ]
+  },
+  {
+    "cmd": [
+      "python",
+      "-u",
       "[SLAVE_BUILD]/src/testing/scripts/get_compile_targets.py",
       "--output",
       "/path/to/tmp/json",