Add pshmakov@ to custom tabs-related owners files

R=peconn, mvanouwerkerk

Change-Id: I133b381279d1765fe86026089c3c6d91bf7a0df0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1543509Reviewed-by: Michael van Ouwerkerk <mvanouwerkerk@chromium.org>
Reviewed-by: Peter Conn <peconn@chromium.org>
Commit-Queue: Peter Beverloo <peter@chromium.org>
Cr-Commit-Position: refs/heads/master@{#645331}

chrome/android/java/src/org/chromium/chrome/browser/browseractions/OWNERS

 mvanouwerkerk@chromium.org
 peconn@chromium.org
+pshmakov@chromium.org
 yusufo@chromium.org
 
 # COMPONENT: UI>Browser>Mobile>CustomTabs

chrome/android/java/src/org/chromium/chrome/browser/browserservices/OWNERS

 lizeb@chromium.org
 mvanouwerkerk@chromium.org
 peconn@chromium.org
+pshmakov@chromium.org
 yusufo@chromium.org
 
 # COMPONENT: UI>Browser>Mobile>CustomTabs

chrome/android/java/src/org/chromium/chrome/browser/customtabs/OWNERS

@@ -2,6 +2,7 @@ lizeb@chromium.org
 mvanouwerkerk@chromium.org
 pasko@chromium.org
 peconn@chromium.org
+pshmakov@chromium.org
 yusufo@chromium.org
 
 # COMPONENT: UI>Browser>Mobile>CustomTabs