GTTF: Enable glibcxx debug mode for Debug builds by default.

This will help us catch problems earlier.

This CL actually fixes several problems detected by this mode.

BUG=65151, 267870, 267891
TEST=none
R=avi@chromium.org, jar@chromium.org, thakis@chromium.org, thestig@chromium.org, yoz@chromium.org

Review URL: https://codereview.chromium.org/22243002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@239811 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 239811