Improve WebSQL's 'openDatabase' exception messages.

This patch flips WebDatabase over to 'es.throwSecurityError()' for those
SecurityError exceptions that appear, and pipes through any error
message that the backend has thrown.

It also drops a few unused (?) error types that mapped to SecurityError.

BUG=152212

Review URL: https://chromiumcodereview.appspot.com/23064015

git-svn-id: svn://svn.chromium.org/blink/trunk@158370 bbb929c8-8fbe-4397-9dbb-9b2b20218538