chromium_tests: pass paths to runit.py and runtest.py for src/testing/scripts

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

 [
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_PACKAGE_REPO[depot_tools]/gclient.py",
       "sync",
       "--verbose",
       "--force",
       "--revision",
@@ skipping 134 matching lines @@
     "cmd": [
       "python",
       "-u",
       "[SLAVE_BUILD]/src/testing/scripts/get_compile_targets.py",
       "--output",
       "/path/to/tmp/json",
       "--",
       "--build-config-fs",
       "Release",
       "--paths",
-      "{\"build\": \"[BUILD]\", \"checkout\": \"[SLAVE_BUILD]/src\"}",
+      "{\"build\": \"[BUILD]\", \"checkout\": \"[SLAVE_BUILD]/src\", \"runit.py\": \"RECIPE_PACKAGE_REPO[build]/scripts/tools/runit.py\", \"runtest.py\": \"RECIPE_PACKAGE_REPO[build]/scripts/slave/runtest.py\"}",
       "--properties",
       "{\"buildername\": \"Chromium Linux Goma Canary\", \"buildnumber\": 571, \"mastername\": \"chromium.fyi\", \"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@@@"
     ]
   },
@@ skipping 114 matching lines @@
     ],
     "cwd": "[SLAVE_BUILD]",
     "name": "content_unittests"
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]