[Android] Add GetDescription and defer calculating device_utc_offset

[Android] Add GetDescription and defer calculating device_utc_offset

First, only get the device's utc offset when it is actually needed. Calculating
this offset takes about 100ms on a typical device. The build scripts assume
that creating an instance of AndroidCommands is not so expensive. Instead,
defer calculating this value until it is actually requested. There are
currently several cases where the build scripts call adb directly instead of
through android_commands just to avoid this extra cost.

Second, add a GetDescription method to get a (mostly) user-readable description
of the device.

TBR=frankf@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=207371

[craigdh, 2013-06-14 20:48:47]

lgtm with nit (frank is OOO today).

https://codereview.chromium.org/17088005/diff/1/build/android/pylib/android_c...
File build/android/pylib/android_commands.py (right):

https://codereview.chromium.org/17088005/diff/1/build/android/pylib/android_c...
build/android/pylib/android_commands.py:853: def DeviceUtcOffset(self):
Maybe GetUtcOffset() for consistency? Should be pretty clear it's on the device
since this is in the AndroidCommands class.

[cjhopman, 2013-06-19 20:01:18]

frankf: TBRed for COMMITTERS

[commit-bot: I haz the power, 2013-06-20 01:49:17]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/cjhopman@chromium.org/17088005/5001

[commit-bot: I haz the power, 2013-06-20 09:09:04]

Change committed as 207371