Add fsamuel@ as OWNER of RenderWidgetHostViewGuest

Bug: none
Change-Id: I5dc0b8be17f8d88fb4650c1c564d7f295dc5c1fe
Reviewed-on: https://chromium-review.googlesource.com/1061575Reviewed-by: Nasko Oskov <nasko@chromium.org>
Commit-Queue: Fady Samuel <fsamuel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#559079}

content/browser/frame_host/OWNERS

 # COMPONENT: Internals>Sandbox>SiteIsolation
+
+# For surface ID propagation and synchronization
+per-file render_widget_host_view_guest*=fsamuel@chromium.org