Removed 'master.' prefix in GCStorage
Removed 'master.' prefix in GCStorage

This makes sure the file name on GCS does not contain a 'master.' prefix.

BUG=376490

Review URL: https://codereview.chromium.org/424303002

git-svn-id: 239fca9b83025a0b6f823aeeca02ba5be3d9fd76@286565 0039d316-1c4b-4281-b951-d872f2087c98

eunchong/build,eunchong/build,eunchong/build,eunchong/build