Add perf_diff to crosperf

Test: perf_diff works with sample report

PRESUBMIT=passed
R=asharif,shenhan,llozano
APPROVED=asharif
DELTA=343  (322 added, 7 deleted, 14 changed)
OCL=63852-p2
RCL=64029-p2
RDATE=2012/11/13 16:10:40


P4 change: 42799246
3 files changed
tree: f934c512a97355d628262aa5c4b9b9e3dbc45edd
  1. .git5_specs/
  2. v14/