POSIX: read subprocess output before waiting for termination.
POSIX: read subprocess output before waiting for termination.

Previously, GetAppOutput was designed only for fuser. However, it
appears that Mac is using it to read the output of ps: which outputs
rather more. In this case, ps can fill up the pipe buffer while we are
waiting for it to exit, leading to deadlock depending on how many other
process are running on the system at the time.

http://codereview.chromium.org/118514


git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@18068 0039d316-1c4b-4281-b951-d872f2087c98

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