Suppress IO-on-wrong-thread DCHECK during file downloads.
Suppress IO-on-wrong-thread DCHECK during file downloads.

BUG=72740
TEST=Downloading a file in linux Debug build should not die with a DCHECK 
failure.

Review URL: http://codereview.chromium.org/6473004

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@74856 0039d316-1c4b-4281-b951-d872f2087c98

adobe/chromium,Crystalnix/house-of-life-chromium,gavinp/chromium,gavinp/chromium,ropik/chromium,Crystalnix/house-of-life-chromium,adobe/chromium,gavinp/chromium,yitian134/chromium,adobe/chromium,yitian134/chromium,Crystalnix/house-of-life-chromium,Crystalnix/house-of-life-chromium,Crystalnix/house-of-life-chromium,gavinp/chromium,yitian134/chromium,yitian134/chromium,adobe/chromium,ropik/chromium,Crystalnix/house-of-life-chromium,Crystalnix/house-of-life-chromium,yitian134/chromium,adobe/chromium,ropik/chromium,ropik/chromium,ropik/chromium,adobe/chromium,yitian134/chromium,gavinp/chromium,adobe/chromium,gavinp/chromium,ropik/chromium,adobe/chromium,yitian134/chromium,adobe/chromium,gavinp/chromium,ropik/chromium,yitian134/chromium,adobe/chromium,Crystalnix/house-of-life-chromium,Crystalnix/house-of-life-chromium,gavinp/chromium,yitian134/chromium,Crystalnix/house-of-life-chromium,gavinp/chromium,ropik/chromium,ropik/chromium,adobe/chromium,Crystalnix/house-of-life-chromium,gavinp/chromium,yitian134/chromium