Move libvpx from DEPS to src

third_party/libvpx/source/libvpx/keywords.dox

Index: third_party/libvpx/source/libvpx/keywords.dox
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+/*!\page rfc2119 RFC2119 Keywords
+
+      The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
+      NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and
+      "OPTIONAL" in this document are to be interpreted as described in
+      <a href="http://www.ietf.org/rfc/rfc2119.txt">RFC 2119.</a>
+
+Specifically, the following definitions are used:
+
+\section MUST
+\anchor REQUIRED
+\anchor SHALL
+   This word, or the terms "REQUIRED" or "SHALL", mean that the
+   definition is an absolute requirement of the specification.
+
+\section MUSTNOT MUST NOT
+\anchor SHALLNOT
+   This phrase, or the phrase "SHALL NOT", mean that the
+   definition is an absolute prohibition of the specification.
+
+\section SHOULD
+\anchor RECOMMENDED
+   This word, or the adjective "RECOMMENDED", mean that there
+   may exist valid reasons in particular circumstances to ignore a
+   particular item, but the full implications must be understood and
+   carefully weighed before choosing a different course.
+
+\section SHOULDNOT SHOULD NOT
+\anchor NOTRECOMMENDED
+   This phrase, or the phrase "NOT RECOMMENDED" mean that
+   there may exist valid reasons in particular circumstances when the
+   particular behavior is acceptable or even useful, but the full
+   implications should be understood and the case carefully weighed
+   before implementing any behavior described with this label.
+
+\section MAY
+\anchor OPTIONAL
+   This word, or the adjective "OPTIONAL", mean that an item is
+   truly optional.  One vendor may choose to include the item because a
+   particular marketplace requires it or because the vendor feels that
+   it enhances the product while another vendor may omit the same item.
+   An implementation which does not include a particular option \ref MUST be
+   prepared to interoperate with another implementation which does
+   include the option, though perhaps with reduced functionality. In the
+   same vein an implementation which does include a particular option
+   \ref MUST be prepared to interoperate with another implementation which
+   does not include the option (except, of course, for the feature the
+   option provides.)
+
+
+*/