Enable parsing of MP4 'cbcs' boxes for desktop Chrome

MP4 'cbcs' boxes specify an encryption scheme when used with encrypted
media. Although the current CDMs don't support this scheme, it will in
the future so enable desktop builds to parse these headers and pass it
to the CDM.

BUG=658026
TEST=existing 'cbcs' browser_tests still pass

Change-Id: I6dc6c1596cf6bd1ecd776877fe45b5908fea4dce
Reviewed-on: https://chromium-review.googlesource.com/1041266
Commit-Queue: John Rummell <jrummell@chromium.org>
Reviewed-by: Xiaohan Wang <xhwang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#555926}

media/media_options.gni

@@ -58,9 +58,9 @@ declare_args() {
   enable_mse_mpeg2ts_stream_parser =
       (proprietary_codecs && is_chromecast) || use_fuzzing_engine
 
-  # Enable support for the 'cbcs' encryption scheme added by MPEG Common
+  # Enable parsing for the 'cbcs' encryption scheme added by MPEG Common
   # Encryption 3rd Edition (ISO/IEC 23001-7), published 02/15/2016.
-  enable_cbcs_encryption_scheme = is_chromecast
+  enable_cbcs_encryption_scheme = is_chromecast || is_mac || is_win || is_linux
 
   # Enable HEVC/H265 demuxing. Actual decoding must be provided by the
   # platform. Enable by default for Chromecast.