Implement mapping randomization for 64-bit Linux. Notes:

Implement mapping randomization for 64-bit Linux. Notes:
- 32-bit Linux already seems to scatter the mmap() chunks around; 64-bit didn't.
- Seed the system random number generator a little better (we needlessly
trunctaed microsecond resolution to millisecond resolution).

[Chris Evans, 2011-07-14 20:38:14]

Here's better ASLR for 64-bit Linux. It'll automatically take advantage of the
better entropy when we pass that in, too.

[Chris Evans, 2011-07-14 21:56:49]

On 2011/07/14 20:38:14, Chris Evans wrote:
> Here's better ASLR for 64-bit Linux. It'll automatically take advantage of the
> better entropy when we pass that in, too.

Closing.
Superceded by http://codereview.chromium.org/7377008/