V8: Switch msan configurations to what chromium uses

scripts/slave/recipes/v8.expected/full_tryserver_v8_v8_linux64_msan_rel.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_MODULE[depot_tools::bot_update]/resources/bot_update.py",
       "--master",
       "tryserver.v8",
       "--builder",
       "v8_linux64_msan_rel",
@@ skipping 130 matching lines @@
     "cmd": [
       "python",
       "-u",
       "RECIPE_PACKAGE_REPO[depot_tools]/gclient.py",
       "runhooks"
     ],
     "cwd": "[SLAVE_BUILD]/v8",
     "env": {
       "GOMA_SERVICE_ACCOUNT_JSON_FILE": "/creds/service_accounts/service-account-goma-client.json",
       "GYP_CHROMIUM_NO_ACTION": "1",
-      "GYP_DEFINES": "clang=1 dcheck_always_on=0 fastbuild=1 gomadir='[CACHE]/cipd/goma' msan=1 target_arch=x64 test_isolation_mode=prepare use_goma=1 v8_target_arch=arm64",
+      "GYP_DEFINES": "clang=1 dcheck_always_on=0 fastbuild=1 gomadir='[CACHE]/cipd/goma' msan=1 msan_track_origins=2 target_arch=x64 test_isolation_mode=prepare use_goma=1 use_prebuilt_instrumented_libraries=1 v8_target_arch=arm64",

[Michael Achenbach, 2016/07/29 11:30:36]

This is set at hooks time because this script needs it:
https://cs.chromium.org/chromium/src/DEPS?q=instrumented_libraries&sq=package...

https://cs.chromium.org/chromium/src/third_party/instrumented_libraries/scrip...

       "GYP_GENERATORS": "ninja",
       "PATH": "%(PATH)s:RECIPE_PACKAGE_REPO[depot_tools]"
     },
     "name": "gclient runhooks"
   },
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_PACKAGE_REPO[build]/scripts/tools/runit.py",
@@ skipping 628 matching lines @@
       "@@@STEP_LOG_LINE@durations@Duration: 00:00:101@@@",
       "@@@STEP_LOG_END@durations@@@"
     ]
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]