Invalidate MallocExtension::GetBytesAllocatedOnCurrentThread if !USE_TCMALLOC.

This check is required to enable gperftools' heap-profiler without the tcmalloc
memory allocator. See the bug for the details.

BUG=341349
TEST=None

Review URL: https://codereview.chromium.org/157233002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@250130 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 250130