Suppress memory error in webcrypto

BUG=348629
TBR=padolph@netflix.com

Review URL: https://codereview.chromium.org/183893040

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@255364 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 255364