Upstream cherry-picks:
  d59820f6fec3fd112436fb7712e4f9d6d768b664 - avformat/matroskadec seek bug fix.
  8efaee3710baa87af40556a622bf2d96a27c6425 - avformat/oggparseopus security fix.
  542f725964e52201000ec34e2f23229cf534ad3a - avformat/oggdec security fix.
  ea791c080dd5494b3bee0c618a3f52e371b5f320 - avformat/utils security fix.
  2875745d354ab0ebc4af1ebaca5c5a8d26ccdc03 - avformat/utils security fix v2.
  17d320800b70a78f4e90cd96564154e829db8b8d - avformat/movenc security fix.
  1a82d2cf8fb6a7e854e7548dfcf73c3d046b34ac - avformat/oggparseopus security fix.
  c1ed78a591f68f3c81eded0bfaac313937ffa3b6 - avformat/utils security fix.
  2be3007ed55f1513bcae3d2a076e71878f48eb03 - avformat/utils security fix.
  7e01d48cfd168c3dfc663f03a3b6a98e0ecba328 - avformat/mov security fix.
  a867b948ed35b3f5b72ee714232c21d5f591e7aa - avformat/oggdec security fix.

Autorename:
  autorename_* files are renamed copies of various files that would cause
    base name collisions from mac libtool. These files are generated
    by generate_gyp.py. https://chromium-review.googlesource.com/#/c/274543/

Current patches:
  .gitignore has a "Chromium stuff" section.

  Changes to configure
    Commented out a section that creates symlink for source_path. Using symlink
    causes windows builds to fail (cl.exe cant find the files).

  Remove add_cflags "-mips64" from configure
    This conflicts with --extra-cflags=-mips64r6 for mips64el. There are a
    series of upstream patches changing how mips arch selection works, this may
    be resolved shortly. (Those patches are not by Google though, and are also
    the reason it broke.)

  Changes/additions to compat/msvcrt/{snprintf.c,snprintf.h}
  Changes/additions to compat/{strtod.c,strtod.h}
    Commit b5269bfb48c71fe17c02eee00c71b1e9762497db changes these files and
    relevant build rules to fix inconsistent linkage when building with MSVC.
    The rules/files expose overriden symbols as externs and force inject these
    headers when building with the component build.
    strtod.h was added, so it may not appear in diffs that ignore additions.
    f3299330654ac1b40c50b3cbcae619f42eb7d838 added an include to snprintf.c.

  Fix pthreads emulation on Windows XP (compat/w32pthreads.h & libavcodec/vp8.c)
    Emulation assumes Vista+ inside (_WIN32_WINNT >= 0x0600) checks. Replace
    with WINDOWS_XP_SUPPORT_NEEDED define in compat/w32pthreads.h.

    Add call to w32thread_init() in libavcodec/vp8.c.

  Remove UNCHECKED_BITSTREAM_READER defines in libavcodec/
    Remove "#define UNCHECKED_BITSTREAM_READER 1" from all codecs.
    In Chromium, all codecs should use the safe bitstream reader.

  Changes to libavcodec/utils.c
    Disable deprecation warnings related to FF_API_AVPACKET_OLD_API.
    We cannot just disable FF_API_AVPACKET_OLD_API because upstream does not yet
    compile with it disabled. Therefore, suppress the warnings locally.

  Revert 'sidx' processing for .mov containers. (libavformat/isom.h and mov.c)
    Reverts commit 4ab56667594842283dc5ae07f0daba2a2cb4d3af.
    'sidx' box processing is broken for MOV containers. http://crbug.com/568336.
    Reported: http://ffmpeg.org/pipermail/ffmpeg-devel/2015-December/185040.html

  Changes to libavformat/matroskadec.c
    Add CONFIG_LZO and CONFIG_SIPR_DECODER (and other CONFIG_*) checks to remove
    code that may be a security risk. Discuss with cevans@ before removing.

    Remove extra const from static EbmlSyntax arrays. This fixes windows
    compile error C4114, since EbmlSyntax struct is already defined with const.
    TODO: push upstream.

    Add call to matroska_read_close() to mitigate memory leak caught by
    Valgrind.

  Changes to libavformat/mp3dec.c
    TODO(chcunningham/dalecurtis): https://crbug.com/504623 - Determine whether
    these changes are still necessary and either remove or document them.

  Changes to libavutil/arm/intmath.h
    Remove static av_always_inline av_const unsigned av_clip_uintp2_arm() and
    av_clip_intp2_arm() due to compilation failure.

  Disable FMA3 instructions in libavutil/log.c (http://crbug.com/440892)
    Remove call to _set_FMA3_enable() on Windows.
    TODO: Remove once Chromium requires VS2015.

  Changes to libavutil/mem.c
    Enable av_max_alloc(0) to remove alloc size bound.

  Changes to libavutil/timer.h
    C++11 compatability for string concatenation (http://crbug.com/454590).
    Add spaces between string literals and tokens.

  Changes/additions to libavutil/x86/x86inc.asm
    https://chromium-review.googlesource.com/#/c/272274/
    Fixes the conditionals on Linux so that these symbols are hidden and
    adds the Chromium-specific private_extern extension for hiding these
    symbols on OSX.

  Changes to libavformat/riffdec.c
    Work around VC++ 2015 Update 1 compiler bug, crbug.com/581768 and
    https://connect.microsoft.com/VisualStudio/feedback/details/2291638