bisect-builds.py: Use Google Common Data Storage instead of build.chromium.org.
bisect-builds.py: Use Google Common Data Storage instead of build.chromium.org.

The continuous archive's index file appears to be incomplete/problematic for
some platforms and revision ranges, so go back to just using directory lists
via the CDS API.

This also cleans up the code by using a PathContext object rather than a slew of
global variables to format/create the various URLs.

BUG=85498
TEST=See bug.

Review URL: http://codereview.chromium.org/6995117

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@88658 0039d316-1c4b-4281-b951-d872f2087c98

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