[toolchain-utils] Add new script for generating waterfall reports.

There are still things that should be done to improve this, but the
basic script is working now.

BUG=chromium:649175
TEST=Tested extensively in my account.

Change-Id: I4b0e833d635047293b74b7971a1b5d3f2676b440
Reviewed-on: https://chrome-internal-review.googlesource.com/305905
Commit-Ready: Caroline Tice <cmtice@google.com>
Tested-by: Caroline Tice <cmtice@google.com>
Reviewed-by: Yunlian Jiang <yunlian@google.com>
1 file changed