Check the EE's eKU extension field, if present.

BUG=https://code.google.com/p/chromium/issues/detail?id=167607 and
https://b.corp.google.com/issue?id=7920492

(cherry picked from commit 0da1515c5fe4e97fc2d4d24a41ebd4c078fec4db)

Change-Id: I4309d4a90a9d41390f41c748fa1442ed736e225f
4 files changed