Revert r249112: "[webcrypto] Require optional JWK properties to have the correct type."

(It triggered an uninitialized memory error on Mac Valgrind bot.)

Review URL: https://codereview.chromium.org/150663011

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@249270 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 249270