linux: enable PIE (ASLR) for chrome executable

      I had been concerned that this wouldn't work with our -fPIC
bits we build internally, but the difference is actually a
performance once, not a correctness one.

(Retry of r85286, with ARM and ia32 disabled.)

BUG=57908

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=85437

Review URL: http://codereview.chromium.org/6973032

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@86333 0039d316-1c4b-4281-b951-d872f2087c98