Add support for "additional_mirrors" property in trybot configs.

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

 [
   {
     "cmd": [
       "python",
       "-u",
       "[BUILD]/scripts/slave/bot_update.py",
       "--master",
-      "chromium.linux",
+      "chromium.gpu",
       "--builder",
-      "Linux Tests",
+      "Linux Release (NVIDIA)",
       "--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'}]",
       "--root",
       "src",
       "--revision_mapping_file",
       "{\"src\": \"got_revision\", \"src/native_client\": \"got_nacl_revision\", \"src/third_party/angle\": \"got_angle_revision\", \"src/third_party/webrtc\": \"got_webrtc_revision\", \"src/tools/swarming_client\": \"got_swarming_client_revision\", \"src/v8\": \"got_v8_revision\"}",
       "--output_json",
       "/path/to/tmp/json",
@@ skipping 93 matching lines @@
       "GYP_CHROMIUM_NO_ACTION": "1",
       "GYP_DEFINES": "component=static_library gomadir='[BUILD]/goma' target_arch=x64 test_isolation_mode=prepare use_goma=1"
     },
     "name": "gclient runhooks"
   },
   {
     "cmd": [
       "python",
       "-u",
       "\nimport shutil\nimport sys\nshutil.copy(sys.argv[1], sys.argv[2])\n",
-      "[SLAVE_BUILD]/src/testing/buildbot/chromium.linux.json",
+      "[SLAVE_BUILD]/src/testing/buildbot/chromium.gpu.json",
       "/path/to/tmp/json"
     ],
     "cwd": "[SLAVE_BUILD]",
     "name": "read test spec",
     "~followup_annotations": [
-      "@@@STEP_TEXT@path: [SLAVE_BUILD]/src/testing/buildbot/chromium.linux.json@@@",
+      "@@@STEP_TEXT@path: [SLAVE_BUILD]/src/testing/buildbot/chromium.gpu.json@@@",
       "@@@STEP_LOG_LINE@json.output@{@@@",
-      "@@@STEP_LOG_LINE@json.output@  \"Linux Tests\": {@@@",
+      "@@@STEP_LOG_LINE@json.output@  \"Linux Release (NVIDIA)\": {@@@",
       "@@@STEP_LOG_LINE@json.output@    \"gtest_tests\": [@@@",
       "@@@STEP_LOG_LINE@json.output@      {@@@",
       "@@@STEP_LOG_LINE@json.output@        \"swarming\": {@@@",
       "@@@STEP_LOG_LINE@json.output@          \"can_use_on_swarming_builders\": true@@@",
       "@@@STEP_LOG_LINE@json.output@        }, @@@",
       "@@@STEP_LOG_LINE@json.output@        \"test\": \"browser_tests\"@@@",
       "@@@STEP_LOG_LINE@json.output@      }@@@",
       "@@@STEP_LOG_LINE@json.output@    ]@@@",
       "@@@STEP_LOG_LINE@json.output@  }@@@",
       "@@@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",
       "--",
       "--build-config-fs",
       "Release",
       "--use-src-side-runtest-py",
       "--paths",
       "{\"build\": \"[BUILD]\", \"checkout\": \"[SLAVE_BUILD]/src\"}",
       "--properties",
-      "{\"buildername\": \"Linux Tests\", \"buildnumber\": 571, \"mastername\": \"chromium.linux\", \"slavename\": \"TestSlavename\", \"target_platform\": \"linux\"}"
+      "{\"buildername\": \"Linux Release (NVIDIA)\", \"buildnumber\": 571, \"mastername\": \"chromium.gpu\", \"slavename\": \"TestSlavename\", \"target_platform\": \"linux\"}"
     ],
     "cwd": "[SLAVE_BUILD]",
     "name": "get compile targets for scripts",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@json.output@{}@@@",
       "@@@STEP_LOG_END@json.output@@@"
     ]
   },
   {
     "cmd": [
@@ skipping 26 matching lines @@
   {
     "cmd": [
       "python",
       "-u",
       "[BUILD]/scripts/slave/extract_build.py",
       "--target",
       "Release",
       "--build-archive-url",
       "gs://test-domain/test-archive.zip",
       "--master-name",
-      "chromium.linux",
+      "chromium.gpu",
       "--build-number",
       "571"
     ],
     "cwd": "[SLAVE_BUILD]",
     "name": "extract build"
   },
   {
     "cmd": [
       "python",
       "-u",
@@ skipping 22 matching lines @@
       "trigger",
       "--swarming",
       "https://chromium-swarm.appspot.com",
       "--isolate-server",
       "https://isolateserver.appspot.com",
       "--priority",
       "25",
       "--shards",
       "1",
       "--task-name",
-      "browser_tests/Ubuntu-12.04/ffffffffff/Linux Tests/571",
+      "browser_tests/Ubuntu-12.04/ffffffffff/Linux Release (NVIDIA)/571",
       "--dump-json",
       "/path/to/tmp/json",
       "--expiration",
       "3600",
       "--io-timeout",
       "1200",
       "--hard-timeout",
       "3600",
       "--dimension",
       "cpu",
       "x86-64",
       "--dimension",
       "gpu",
       "none",
       "--dimension",
       "os",
       "Ubuntu-12.04",
       "--dimension",
       "pool",
       "Chrome",
       "--tag",
-      "buildername:Linux Tests",
+      "buildername:Linux Release (NVIDIA)",
       "--tag",
       "buildnumber:571",
       "--tag",
       "data:ffffffffffffffffffffffffffffffffffffffff",
       "--tag",
-      "master:chromium.linux",
+      "master:chromium.gpu",
       "--tag",
       "name:browser_tests",
       "--tag",
       "os:Ubuntu-12.04",
       "--tag",
       "project:chromium",
       "--tag",
       "purpose:CI",
       "--tag",
       "purpose:post-commit",
       "--tag",
       "slavename:TestSlavename",
       "--tag",
       "stepname:browser_tests",
       "--idempotent",
       "ffffffffffffffffffffffffffffffffffffffff",
       "--",
       "--test-launcher-summary-output=${ISOLATED_OUTDIR}/output.json"
     ],
     "cwd": "[SLAVE_BUILD]",
     "name": "[trigger] browser_tests",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@json.output@{@@@",
-      "@@@STEP_LOG_LINE@json.output@  \"base_task_name\": \"browser_tests/Ubuntu-12.04/ffffffffff/Linux Tests/571\", @@@",
+      "@@@STEP_LOG_LINE@json.output@  \"base_task_name\": \"browser_tests/Ubuntu-12.04/ffffffffff/Linux Release (NVIDIA)/571\", @@@",
       "@@@STEP_LOG_LINE@json.output@  \"tasks\": {@@@",
-      "@@@STEP_LOG_LINE@json.output@    \"browser_tests/Ubuntu-12.04/ffffffffff/Linux Tests/571\": {@@@",
+      "@@@STEP_LOG_LINE@json.output@    \"browser_tests/Ubuntu-12.04/ffffffffff/Linux Release (NVIDIA)/571\": {@@@",
       "@@@STEP_LOG_LINE@json.output@      \"shard_index\": 0, @@@",
       "@@@STEP_LOG_LINE@json.output@      \"task_id\": \"10000\", @@@",
       "@@@STEP_LOG_LINE@json.output@      \"view_url\": \"https://chromium-swarm.appspot.com/user/task/10000\"@@@",
       "@@@STEP_LOG_LINE@json.output@    }@@@",
       "@@@STEP_LOG_LINE@json.output@  }@@@",
       "@@@STEP_LOG_LINE@json.output@}@@@",
       "@@@STEP_LOG_END@json.output@@@",
       "@@@STEP_LINK@shard #0@https://chromium-swarm.appspot.com/user/task/10000@@@"
     ]
   },
@@ skipping 10 matching lines @@
       "--merged-test-output",
       "/path/to/tmp/json",
       "--",
       "collect",
       "--swarming",
       "https://chromium-swarm.appspot.com",
       "--decorate",
       "--print-status-updates",
       "--shards",
       "1",
-      "browser_tests/Ubuntu-12.04/ffffffffff/Linux Tests/571"
+      "browser_tests/Ubuntu-12.04/ffffffffff/Linux Release (NVIDIA)/571"
     ],
     "cwd": "[SLAVE_BUILD]",
     "name": "browser_tests"
   },
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_MODULE[test_results]/resources/upload_gtest_test_results.py",
       "--input-gtest-json",
       "{\"per_iteration_data\": [{\"Test.One\": [{\"elapsed_time_ms\": 0, \"output_snippet\": \"\", \"status\": \"SUCCESS\"}], \"Test.Three\": [{\"elapsed_time_ms\": 0, \"output_snippet\": \"\", \"status\": \"SUCCESS\"}], \"Test.Two\": [{\"elapsed_time_ms\": 0, \"output_snippet\": \"\", \"status\": \"SUCCESS\"}]}]}",
       "--master-name",
-      "chromium.linux",
+      "chromium.gpu",
       "--builder-name",
-      "Linux Tests",
+      "Linux Release (NVIDIA)",
       "--build-number",
       "571",
       "--test-type",
       "browser_tests",
       "--test-results-server",
       "test-results.appspot.com",
       "--chrome-revision",
       "170242"
     ],
     "cwd": "[SLAVE_BUILD]",
     "name": "Upload to test-results [browser_tests]"
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]