Add DoNotDropColorBitmapTables() API.

Adding a API not to drop CBDT/CBLC tables. OTS doesn't recognize the tables
for now, but trusts users of this API, assuming users exactly know the risks.

BUG=324187
R=ksakamoto@chromium.org

Review URL: https://codereview.chromium.org/341983012
Add BUILD.gn

TBR=ksakamoto@chromium,org, brett@chromium.org

Review URL: https://codereview.chromium.org/341393006