[webcrypto] Remove a special case for AES-KW wrapping/unwrapping.

Now the same export+encrypt / decrypt+import codepath is used as for other wrapping algorithms.

The new code is less efficient (creates a temporary raw key), however simplifies things, and allows wrapping to be done on non-raw keys (however because of size constraints is likely to fail).

BUG=373544,245025

Review URL: https://codereview.chromium.org/335463002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@276890 0039d316-1c4b-4281-b951-d872f2087c98
4 files changed