Build: https://chromium-swarm.appspot.com/task?id=40fde71e1d532610&refresh=10&show_raw=1

"""
*** Error in `python': free(): invalid pointer: 0x00007feac0000078 ***
======= Backtrace: =========
/lib/x86_64-linux-gnu/libc.so.6(+0x777e5)[0x7feaebc2e7e5]
/lib/x86_64-linux-gnu/libc.so.6(+0x8037a)[0x7feaebc3737a]
/lib/x86_64-linux-gnu/libc.so.6(cfree+0x4c)[0x7feaebc3b53c]
python(PyThread_ReInitTLS+0x81)[0x50b0c1]
python(PyOS_AfterFork+0x37)[0x511757]
python[0x5fce86]
python(PyEval_EvalFrameEx+0x6efa)[0x4c449a]
python(PyEval_EvalCodeEx+0x7f8)[0x4c6a88]
python(PyEval_EvalFrameEx+0x6cd1)[0x4c4271]
python(PyEval_EvalCodeEx+0x7f8)[0x4c6a88]
python[0x6278ff]
python(PyObject_Call+0x3a)[0x42e56a]
python[0x432a55]
python(PyObject_Call+0x3a)[0x42e56a]
python[0x48ff3f]
python[0x48ae1a]
python(PyObject_Call+0x3a)[0x42e56a]
python(PyEval_EvalFrameEx+0x1805)[0x4beda5]
python(PyEval_EvalCodeEx+0x7f8)[0x4c6a88]
python(PyEval_EvalFrameEx+0x6cd1)[0x4c4271]
python(PyEval_EvalCodeEx+0x7f8)[0x4c6a88]
python(PyEval_EvalFrameEx+0x6cd1)[0x4c4271]
python(PyEval_EvalFrameEx+0x71f6)[0x4c4796]
python(PyEval_EvalCodeEx+0x7f8)[0x4c6a88]
python(PyEval_EvalFrameEx+0x6cd1)[0x4c4271]
python(PyEval_EvalCodeEx+0x7f8)[0x4c6a88]
python[0x6278ff]
python(PyObject_Call+0x3a)[0x42e56a]
python(PyEval_EvalFrameEx+0x213b)[0x4bf6db]
python(PyEval_EvalFrameEx+0x71f6)[0x4c4796]
python(PyEval_EvalFrameEx+0x71f6)[0x4c4796]
python(PyEval_EvalCodeEx+0x7f8)[0x4c6a88]
python[0x627830]
python(PyObject_Call+0x3a)[0x42e56a]
python[0x432a55]
python(PyObject_Call+0x3a)[0x42e56a]
python(PyEval_CallObjectWithKeywords+0x47)[0x4bd4f7]
python[0x50f602]
/lib/x86_64-linux-gnu/libpthread.so.0(+0x76ba)[0x7feaec8d06ba]
/lib/x86_64-linux-gnu/libc.so.6(clone+0x6d)[0x7feaebcbe41d]
======= Memory map: ========
00400000-00be0000 r-xp 00000000 08:02 12583877                           /b/swarming/w/ir/.swarming_module_cache/vpython/94cf0d/bin/python2.7
00de0000-00e02000 r-xp 007e0000 08:02 12583877                           /b/swarming/w/ir/.swarming_module_cache/vpython/94cf0d/bin/python2.7
00e02000-014d5000 rwxp 00802000 08:02 12583877                           /b/swarming/w/ir/.swarming_module_cache/vpython/94cf0d/bin/python2.7
"""

Searching on Google gets 1 other result:
http://mercurial.808500.n3.nabble.com/Bug-5554-New-Error-in-python-free-invalid-pointer-0x00007ff368007640-when-running-tests-td4051976.html