AppCache: Add myself as an OWNER for AppCache files in content/common.

This will facilitate AppCache Onion Souping reviews.

Bug: 611938
Change-Id: Ifa8ca2899855584e1c400ada364618b259744bd5
Reviewed-on: https://chromium-review.googlesource.com/c/1392282Reviewed-by: Avi Drissman <avi@chromium.org>
Commit-Queue: Avi Drissman <avi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#619282}

content/common/OWNERS

@@ -44,3 +44,7 @@ per-file accessibility_node_data.*=dtseng@chromium.org
 # DirectWrite
 per-file dwrite_font_platform_win*=scottmg@chromium.org
 per-file font_warmup_win.cc=scottmg@chromium.org
+
+# AppCache
+per-file appcache_interfaces.h=pwnall@chromium.org
+per-file appcache_interfaces.cc=pwnall@chromium.org