Add xidle library to power_manager for testing how long the user has been idle

Add xidle library to power_manager for testing how long the user has been idle
BUG=none
TEST=included

[rtc, 2010-02-26 08:01:33]

Please look at and fix the lint warnings as well.

http://codereview.chromium.org/652147/diff/1/3
File src/platform/power_manager/xidle-test.cc (right):

http://codereview.chromium.org/652147/diff/1/3#newcode8
src/platform/power_manager/xidle-test.cc:8: int main(int argc, char *argv[]) {
Could this be a GTest instead (Google wrappers around cppunit)?

http://codereview.chromium.org/652147/diff/1/5
File src/platform/power_manager/xidle.h (right):

http://codereview.chromium.org/652147/diff/1/5#newcode17
src/platform/power_manager/xidle.h:17: // Creating a new XIdle object connects
to the local X Server.
A small nit. Could you add a sample usage to the header comments?

http://codereview.chromium.org/652147/diff/1/5#newcode22
src/platform/power_manager/xidle.h:22: Display *display;
Member variables should end with an underscore. You should disable the copy
constructor as well. 

If you haven't already checked it out, our C++ style guide is here.
http://google-styleguide.googlecode.com/svn/trunk/cppguide.xml

[rtc, 2010-03-08 18:55:54]

LGTM