CdmWrapper cleanups.

- Add cdm_helper.h to hold types used by CdmWrapper.
- Add cdm_wrapper.h to separate declaration and definition.
- Rename CdmWrapper to CdmAdater to better match the binary name, which is
  "*cdmadapter.*".

BUG=306647
TEST=none
R=dalecurtis@chromium.org, ddorwin@chromium.org

Review URL: https://codereview.chromium.org/27774002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@229494 0039d316-1c4b-4281-b951-d872f2087c98
[Net] Separate out NUM_PRIORITIES from RequestPriority enum

Introduce MAXIMUM_PRIORITY instead and use this when appropriate.

This is so that one can assume that a RequestPriority instance contains
only a valid priority.

BUG=307757
R=rch@chromium.org
TBR=simonjam@chromium.org

Review URL: https://codereview.chromium.org/27213004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@229495 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 229494
SVN changes up to revision 229495