Update documentation for "COMMIT=false".

The meaning of "COMMIT=false" was changed in https://code.google.com/p/chromium/issues/detail?id=470609.
I have also updated the corresponding Chromium documentation in https://sites.google.com/a/chromium.org/dev/developers/testing/commit-queue

BUG=skia:
NOTRY=true
DOCS_PREVIEW= https://skia.org/?cl=1107343004

Review URL: https://codereview.chromium.org/1107343004
1 file changed