[pgo/linux] prepare linux for profile consumption

Appending linux as a supproted platform for the update pgo script.
Adding the linux.pgo.txt with the latest profile information.

Bug: 1105530
Change-Id: I63ec40b915970d9ad8a06aaaf594dcbf96dad109
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2347070
Commit-Queue: Jeff Yoon <jeffyoon@chromium.org>
Commit-Queue: Yuke Liao <liaoyuke@chromium.org>
Auto-Submit: Jeff Yoon <jeffyoon@chromium.org>
Reviewed-by: Yuke Liao <liaoyuke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#796521}

chrome/build/linux.pgo.txt

+chrome-linux-master-1597082402-c5bd486642405d828e9e780a3fe4cf0c960a0b58.profdata

tools/update_pgo_profiles.py

@@ -132,7 +132,7 @@ def main():
   parser.add_argument(
       '--target',
       required=True,
-      choices=['win32', 'win64', 'mac'],
+      choices=['win32', 'win64', 'mac', 'linux'],
       help='Identifier of a specific target platform + architecture.')
   subparsers = parser.add_subparsers()