libwebm: Pull from upstream

Upstream has had some refactoring and hence i'm updating the
makefile to reflect those changes. Also adding a
README.android documenting the procedure for future updates.

Bug: 27681071

Current HEAD: 5c50e310e7050192b952fe588186fd1dadc08b6e

Change-Id: I00e1cffd66dc4f6284a9accc8b63f669d7ac7297
(cherry picked from commit 6a8330e5684abb81a14e488ebafa283c085c5c79)
5 files changed