Add gab@ to base/OWNERS.

Also sorted existing OWNERS alphabetically (matching
src/OWNERS chrome/OWNERS and content/OWNERS' style).

BUG=None

Review-Url: https://codereview.chromium.org/2597043002
Cr-Commit-Position: refs/heads/master@{#440315}

diff --git a/base/OWNERS b/base/OWNERS
index b58c9bb1..06f165f 100644
--- a/base/OWNERS
+++ b/base/OWNERS

@@ -17,11 +17,12 @@
 # multiple consumers across the codebase, consider placing it in a new directory
 # under components/ instead.
 
+danakj@chromium.org
+dcheng@chromium.org
+gab@chromium.org
 mark@chromium.org
 thakis@chromium.org
-danakj@chromium.org
 thestig@chromium.org
-dcheng@chromium.org
 
 # For Bind/Callback:
 per-file bind*=tzik@chromium.org