Fix incorrect assumption in IDMap and SmallMap tests.

Some of the tests assumed that base::hash_map is ordered, which it is not. They
worked under libstdc++, but broke in libc++ builds.

BUG=327334
R=thakis@chromium.org, brettw@chromium.org
TEST=base_unittests

Review URL: https://codereview.chromium.org/130783003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@246644 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 246644