[NaCl SDK] Remove naclports bundle directory before building.

Previously, a stale file could break the build. In this case, the zlib build
was using an old zlib header to compile the new zlib library.

BUG=none
TEST=ran locally. No trybots because naclports is not built on trybots
R=sbc@chromium.org

Review URL: https://codereview.chromium.org/192483005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@256046 0039d316-1c4b-4281-b951-d872f2087c98
Validate hashes based on the legacy device id from M33 on Windows without generally hurting performance.

Introduces a new validation level (VALID_LEGACY_DEVICE_ID) from PrefHashCalculator and a new UMA histogram to go along with it.

The MAC address gathering code is a pure copy/paste from chrome/browser/extensions/api/music_manager_private/device_id_win.cc from an M33 checkout which is the implementation we want to keep around (see bug for a broader duplicate code justification).

BUG=350028
TEST=Run a chrome with this CL against an M33 User Data dir and confirm that every pref reports Settings.TrackedPreferenceUnchangeLegacyDeviceId (except for kExtensionsPref which is initialized to split pref as expected).
R=asvitkine@chromium.org, erikwright@chromium.org

Review URL: https://codereview.chromium.org/190183002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@256047 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 256047