Chromium: make use of new get_files_affected_by_patch.

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

 [
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_MODULE[depot_tools::bot_update]/resources/bot_update.py",
       "--master",
       "tryserver.blink",
       "--builder",
       "mac_blink_rel",
@@ skipping 214 matching lines @@
       "@@@STEP_LOG_END@json.output@@@"
     ]
   },
   {
     "cmd": [
       "git",
       "diff",
       "--cached",
       "--name-only"
     ],
-    "cwd": "[SLAVE_BUILD]/src",
+    "cwd": "[SLAVE_BUILD]/src/third_party/skia",

[rmistry, 2016/04/29 16:40:45]

This looks much better.

     "name": "git diff to analyze patch",
     "stdout": "/path/to/tmp/",
     "~followup_annotations": [
-      "@@@STEP_LOG_LINE@files@foo.cc@@@",
+      "@@@STEP_LOG_LINE@files@src/third_party/skia/foo.cc@@@",
       "@@@STEP_LOG_END@files@@@",
-      "@@@SET_BUILD_PROPERTY@subproject_tag@\"chromium\"@@@"
+      "@@@SET_BUILD_PROPERTY@subproject_tag@\"blink-paths\"@@@"
     ]
   },
   {
     "cmd": [
       "python",
       "-u",
       "\nimport shutil\nimport sys\nshutil.copy(sys.argv[1], sys.argv[2])\n",
       "[SLAVE_BUILD]/src/testing/buildbot/trybot_analyze_config.json",
       "/path/to/tmp/json"
     ],
@@ skipping 19 matching lines @@
       "python",
       "-u",
       "[SLAVE_BUILD]/src/tools/mb/mb.py",
       "analyze",
       "-m",
       "tryserver.blink",
       "-b",
       "mac_blink_rel",
       "-v",
       "//out/Release",
-      "{\"additional_compile_targets\": [], \"files\": [\"foo.cc\"], \"test_targets\": [\"blink_tests\"]}",
+      "{\"additional_compile_targets\": [], \"files\": [\"third_party/skia/foo.cc\"], \"test_targets\": [\"blink_tests\"]}",
       "/path/to/tmp/json"
     ],
     "env": {
       "GOMA_SERVICE_ACCOUNT_JSON_FILE": "/creds/service_accounts/service-account-goma-client.json"
     },
     "name": "analyze",
     "~followup_annotations": [
       "@@@STEP_TEXT@No compile necessary@@@",
       "@@@STEP_LOG_LINE@json.output@{@@@",
       "@@@STEP_LOG_LINE@json.output@  \"compile_targets\": [], @@@",
@@ skipping 20 matching lines @@
       "import sys; sys.exit(0)"
     ],
     "name": "mark: before_tests"
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]