Protect predictor_ shutdown in PrifileImplIoData::Handle destructor
Protect predictor_ shutdown in PrifileImplIoData::Handle destructor

BUG=20407
TEST=Run browser tests and watch for crashes in shutdown (see issue)

Review URL: http://codereview.chromium.org/8043029

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@102825 0039d316-1c4b-4281-b951-d872f2087c98

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