Added crypto random-number generator

Added a cryptographic random-number generator to crypto/.
Modified sync to use this function instead.
May also be used by Cloud Print in the future.


Review URL: https://chromiumcodereview.appspot.com/10698177

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@149689 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/base/rand_util_posix.cc b/base/rand_util_posix.cc
index abb404a..d65ddae 100644
--- a/base/rand_util_posix.cc
+++ b/base/rand_util_posix.cc
@@ -41,6 +41,7 @@
 
 namespace base {
 
+// NOTE: This function must be cryptographically secure. http://crbug.com/140076
 uint64 RandUint64() {
   uint64 number;