[Mac] Make about:memory not crash.
[Mac] Make about:memory not crash.

http://codereview.chromium.org/177024 enabled about:memory for Linux,
but it went from not-implemented to crashing for Mac, due to an
out-of-bounds vector access.  This returns it to simply not-implemented.

http://crbug.com/21830
TEST=Browse to about:memory, don't crash, show a template with
obviously null data in it.

Review URL: http://codereview.chromium.org/219008

git-svn-id: dd90618784b6a4b323ea0c23a071cb1c9e6f2ac7@26964 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser