metrics: hash the path bytes directly for plugin filename
metrics: hash the path bytes directly for plugin filename

We use the hash of the plugin filename as a unique identifier
for the plugin.  On Windows, this new code produces the same
hashes as before; on Mac/Linux, it saves extra conversions.

BUG=69467

Review URL: http://codereview.chromium.org/6368110

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@74044 0039d316-1c4b-4281-b951-d872f2087c98

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