Make mac toolchain update script print nothing in the happy case where it needs to do nothing.

The script now prints nothing both when it uses a local toolchain and when it
uses a hermetic toolchain that's already up-to-date, but I argue that almost
nobody was looking at that output anyways.

This is part of a few changes to make `gclient runhooks` less noisy.

Bug: 772741
Change-Id: I4f32491894269522617cde7fd180344ae02c43bb
Reviewed-on: https://chromium-review.googlesource.com/709637
Reviewed-by: Erik Chen <erikchen@chromium.org>
Reviewed-by: Justin Cohen <justincohen@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#507770}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 03dff362ace00df6ad8825d1c8baabae5af9de94

mac_toolchain.py

@@ -213,12 +213,10 @@ def RequestGsAuthentication():
 
 def DownloadHermeticBuild(target_os, toolchain_version, toolchain_filename):
   if not _UseHermeticToolchain(target_os):
-    print 'Using local toolchain for %s.' % target_os
     return 0
 
   toolchain_output_path = TOOLCHAIN_BUILD_DIR % target_os
   if ReadStampFile(target_os) == toolchain_version:
-    print 'Toolchain (%s) is already up to date.' % toolchain_version
     FinalizeUnpack(toolchain_output_path, target_os)
     return 0