Add script to search blocked words in repo

Usage: search_blocked_words.sh [/path/to/word_list.txt]

Use case 1: Search all globally blocked words.

  $ search_blocked_words.sh ~/trunk/src/repohooks/blocked_terms.txt

- This is useful when first introducing unblocked_terms.txt to a repo.
- This is also useful to verify the blocked words indeed do not exist.
  Some CLs may have checked in blocked words using '--no-verify' flag
  circumventing the repo check.

Use case 2: Search all words in the local unblock list.

  $ search_blocked_words.sh

- This is useful to learn the current COIL status.

For example, running the script in src/platform2 results in:

reg_exp                #lines  #files  #filenames
black.?hat                  0       0           0
black.?list                47      12           0
build.?cop                  0       0           0
crazy                      12       4           1
cripple                     0       0           0
dummy                     902     186           3
first.?class.?citizen       0       0           0
grandfathered               0       0           0
gr[ae]y.?hat                0       0           0
gr[ae]y.?list               0       0           0
insane                      0       0           0
\bhe\b                     18      12           0
\bshe\b                     2       2           0
\bhim\b                     0       0           0
\bher\b                     0       0           0
\bhis\b                     1       1           0
\bhers\b                    0       0           0
man.?in.?the.?middle        0       0           0
master                   1616     216          16
mitm                       11       6           0
native                    932     238           4
red.?line                   1       1           0
rtfm                        1       1           0
sane                      564      39           5
sanity                    137      77           0
slave                     260      49           1
white.?glove                0       0           0
white.?hat                  0       0           0
white.?label              227      24           0
white.?list               244      59           4
wtf                        26       4           0

BUG=b:165908442
TEST=See above.

Change-Id: Ic0ad12362883435ab33f8eb928f88602dad91375
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/dev-util/+/2404702
Tested-by: Daisuke Nojiri <dnojiri@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Daisuke Nojiri <dnojiri@chromium.org>
Commit-Queue: Daisuke Nojiri <dnojiri@chromium.org>
1 file changed