Silence log spam by json_pref_store.cc:
Silence log spam by json_pref_store.cc:

[41576:263:667661121013959:ERROR:json_pref_store.cc(89)] Error while loading JSON file: File doesn't exist.

This happens a lot in tests that use a fresh profile (most of them do).

BUG=none

Review URL: http://codereview.chromium.org/6966009

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@84687 0039d316-1c4b-4281-b951-d872f2087c98

yitian134/chromium,yitian134/chromium,adobe/chromium,yitian134/chromium,gavinp/chromium,gavinp/chromium,yitian134/chromium,adobe/chromium,yitian134/chromium,adobe/chromium,adobe/chromium,yitian134/chromium,adobe/chromium,adobe/chromium,gavinp/chromium,ropik/chromium,gavinp/chromium,adobe/chromium,ropik/chromium,gavinp/chromium,ropik/chromium,gavinp/chromium,yitian134/chromium,gavinp/chromium,adobe/chromium,gavinp/chromium,adobe/chromium,ropik/chromium,gavinp/chromium,ropik/chromium,yitian134/chromium,ropik/chromium,adobe/chromium,yitian134/chromium,gavinp/chromium,yitian134/chromium,adobe/chromium,ropik/chromium,ropik/chromium,ropik/chromium