Turn on verbose logging for Valgrind_PreAbandonGpuContext bot.

Bug: skia:6575
Change-Id: I0e7d355ff8eea5af78585ef0eef78d509e52d580
Reviewed-on: https://skia-review.googlesource.com/14652
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Ben Wagner <benjaminwagner@google.com>

infra/bots/recipes/test.expected/Test-Ubuntu-GCC-ShuttleA-GPU-GTX550Ti-x86_64-Release-Valgrind_PreAbandonGpuContext.json

@@ -480,6 +480,7 @@
       ".SRW",
       "--match",
       "~Threaded",
+      "--verbose",
       "--preAbandonGpuContext"
     ],
     "env": {

infra/bots/recipes/test.py

@@ -535,6 +535,9 @@ def dm_flags(bot):
       or 'Win8-MSVC-ShuttleB' in bot):
     args.append('--noRAW_threading')
 
+  if 'Valgrind' in bot and 'PreAbandonGpuContext' in bot:
+    args.append('--verbose')
+
   return args