Code:  void TestBlinkPlatformSupport::cryptographicallyRandomValues(
     unsigned char* buffer,
     size_t length) {
 }

Vulnerability Type: 
CWE ID: CWE-310
Summary: Blink, as used in Google Chrome before 48.0.2564.82, does not ensure that a proper cryptographicallyRandomValues random number generator is used, which makes it easier for remote attackers to defeat cryptographic protection mechanisms via unspecified vectors.
Commit Message: Add assertions that the empty Platform::cryptographicallyRandomValues() overrides are not being used.

These implementations are not safe and look scary if not accompanied by an assertion. Also one of the comments was incorrect.

BUG=552749

Review URL: https://codereview.chromium.org/1419293005

Cr-Commit-Position: refs/heads/master@{#359229}