Define static members outside the template class.

When defining a static const member of a template class,
MyClass<T1>::some_static_member and MyClass<T2>::some_static_member
could be different values. We define these values inline in the class,
but ASan complains about an undefined reference.

Since those constants don't depend on the type, This patch moves them
to plain constants in the anonymous namespace.

Bug: chromium:611405
TEST=USE="clang asan" emerge-link update_engine

(cherry picked from commit 857ded12)

Change-Id: Iee4d8d0b919f2a4707d13872f9602f88c9c9fabb