Remove --purge-memory-button.

This was added years ago as a way to test the memory purger, but we never ended
up using the memory purger.  This removes the button and the MemoryPurger class,
but not all the scattered pieces of memory-purging functionality the class could
call.  Those will be removed in subsequent CLs.

BUG=350455
TEST=none
R=sky@chromium.org

Review URL: https://codereview.chromium.org/192573010

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@256072 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 256072
Use absolute nmf root when deciding relative paths.

create_nmf.py generates unusable nmf files when the nmf root is not specified
as an absolute path, because its underlying implementation relies on
os.path.relpath, which expects paths from the same root.

Convert nmf_root to an absolute path when it is initially set.

Note this regressed in r255474:
https://codereview.chromium.org/161613002

BUG=None
TEST=None
R=binji@chromium.org

Review URL: https://codereview.chromium.org/192053002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@256073 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 256073