Add port for libwebm

[GoogleCodeExporter]

Issue #168 (https://code.google.com/p/naclports/issues/detail?id=168) adds 
libvpx. Add libwebm so that we have a container to hold VP8/VP9. This version 
is the latest tagged version in the libwebm repository.

Original issue reported on code.google.com by by...@theclarkfamily.name on 11 Dec 2014 at 9:43

Attachments:

• 0001-Add-port-for-libwebm.patch

[GoogleCodeExporter]

Again thanks.  

Same things apply as for the vpx patch:

In order to accept contributions we need you to sign the CLA:
https://cla.developers.google.com/about/google-individual

Also, if you wouldn't mind uploading your patch using the 'git cl upload' 
command that makes it easier to review and eventually submit (of course we can 
accept the patch file as is, but we prefer to use the code review tool).

Original comment by sbc@google.com on 11 Dec 2014 at 10:06

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[GoogleCodeExporter]

Uploaded for review: https://codereview.chromium.org/817143004

Original comment by by...@theclarkfamily.name on 24 Dec 2014 at 12:34

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