Switch the Mac build from 32-bit to 64-bit.

As of M39, Chrome is a 64-bit only binary. This changes the default build
configuration to 64-bit globally. After this CL, the 32-bit Mac build is no
longer supported.

BUG=405542,18323
R=mark@chromium.org

Review URL: https://codereview.chromium.org/730173002

Cr-Commit-Position: refs/heads/master@{#305043}
2 files changed