Replace instances of vector.data() with &vector[0].

std::vector::data() is only formally defined by C++11, and is not available on the android builds of Chromium.

This change is in anticipation of compiling webcrypto_impl_unittest.cc on Android.

BUG=267888
R=rsleevi@chromium.org

Review URL: https://codereview.chromium.org/24874003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@225672 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 225672