Disable ObjectToString errorprone warning.

See discussion here:
https://groups.google.com/a/chromium.org/forum/#!topic/java/10-nLjh4Rtg

BUG=

Change-Id: Ib2007de8f88edfb08f808eb5f01005cbe975e12b
Reviewed-on: https://chromium-review.googlesource.com/1207653Reviewed-by: Peter Wen <wnwen@chromium.org>
Commit-Queue: Peter Wen <wnwen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#588960}

build/android/gyp/javac.py

@@ -85,6 +85,9 @@ ERRORPRONE_WARNINGS_TO_TURN_OFF = [
   'OverrideThrowableToString',
   # Nice to have better type safety.
   'CollectionToArraySafeParameter',
+  # Makes logcat debugging more difficult, and does not provide obvious
+  # benefits in the Chromium codebase.
+  'ObjectToString',
 ]
 
 ERRORPRONE_WARNINGS_TO_ERROR = [