Fix a crash when delegate_ goes away in ReadStream
Fix a crash when delegate_ goes away in ReadStream

Other callbacks can fire in the context of ReadStream and
OnStopBinding might happen in that context. In this case
the delegate_ is cleaned up and this results in a crash
when ReadStream returns.

BUG=53460
TEST=none

Review URL: http://codereview.chromium.org/3159045

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@57581 0039d316-1c4b-4281-b951-d872f2087c98

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