Better grouping of data in Deep Memory Profiler

In the linux browser profile, put string data under their
own sections, and teach the system about style and css memory.

R=

BUG=

Review URL: https://codereview.chromium.org/148133003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@248996 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 248996
Fix out of bounds avatar index.

Some early supervised user profiles on ChromeOS stored a dummy value of -111 as a Chrome Avatar. We handle this as if
the Chrome Avatar was not chosen yet (which is correct for
these profiles).

BUG=337101

Review URL: https://codereview.chromium.org/136393009

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@248997 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 248997