mac: Make `find_sdk.py --print_sdk_path` much faster.

mac: Make `find_sdk.py --print_sdk_path` much faster.

Use xcrun instead of xcodebuild if --print_sdk_path is passed.  Reduces time
to run `gn gen` from 2.2s to 1.95s on my MacBook Pro.

(In the gyp build, we don't pass --print_sdk_path to this script, so I didn't
notice this script had this slow path until now.)

While here, also stop pretending that we support Xcodes older than 4.3.

BUG=609541
Committed: https://crrev.com/d50140bae570f519cea29a8b20e58511032cbfd7
Cr-Commit-Position: refs/heads/master@{#394565}

[Nico, 2016-05-18 21:04:05]

thakis@chromium.org changed reviewers:
+ rsesek@chromium.org, sdefresne@chromium.org

[Nico, 2016-05-18 21:04:06]

first to stamp wins!

[Robert Sesek, 2016-05-18 21:11:31]

lgtm

[Nico, 2016-05-18 21:12:25]

The CQ bit was checked by thakis@chromium.org

[commit-bot: I haz the power, 2016-05-18 21:12:54]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1988023006/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1988023006/1

[commit-bot: I haz the power, 2016-05-18 22:00:18]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-05-18 22:02:45]

Description was changed from

==========
mac: Make `find_sdk.py --print_sdk_path` much faster.

Use xcrun instead of xcodebuild if --print_sdk_path is passed.  Reduces time
to run `gn gen` from 2.2s to 1.95s on my MacBook Pro.

(In the gyp build, we don't pass --print_sdk_path to this script, so I didn't
notice this script had this slow path until now.)

While here, also stop pretending that we support Xcodes older than 4.3.

BUG=609541
==========

to

==========
mac: Make `find_sdk.py --print_sdk_path` much faster.

Use xcrun instead of xcodebuild if --print_sdk_path is passed.  Reduces time
to run `gn gen` from 2.2s to 1.95s on my MacBook Pro.

(In the gyp build, we don't pass --print_sdk_path to this script, so I didn't
notice this script had this slow path until now.)

While here, also stop pretending that we support Xcodes older than 4.3.

BUG=609541

Committed: https://crrev.com/d50140bae570f519cea29a8b20e58511032cbfd7
Cr-Commit-Position: refs/heads/master@{#394565}
==========

[commit-bot: I haz the power, 2016-05-18 22:02:46]

Patchset 1 (id:??) landed as
https://crrev.com/d50140bae570f519cea29a8b20e58511032cbfd7
Cr-Commit-Position: refs/heads/master@{#394565}

[sdefresne, 2016-05-19 09:18:22]

lgtm

I'm late to the game!