Added SensorManager.getMinDelay()

Exposed the new "min delay" sensor property through native and
java sensor apis. This allows the caller to know what is the
maximum rate at which a sensor can return events, or, if a sensor
works in "update" mode (events returned only when the value changes).

Also augmented SensorManager.regusterSensorEvent() so that it can
accept a value in microsecond in addition to the 4 constants already
defined.

Change-Id: If425e9979892666df8c989d7de3c362230fa19e0
diff --git a/libs/gui/SensorEventQueue.cpp b/libs/gui/SensorEventQueue.cpp
index 4b46842..3396f25 100644
--- a/libs/gui/SensorEventQueue.cpp
+++ b/libs/gui/SensorEventQueue.cpp
@@ -114,10 +114,10 @@
     return mSensorEventConnection->enableDisable(sensor->getHandle(), false);
 }
 
-status_t SensorEventQueue::enableSensor(int32_t handle, int32_t ms) const {
+status_t SensorEventQueue::enableSensor(int32_t handle, int32_t us) const {
     status_t err = mSensorEventConnection->enableDisable(handle, true);
     if (err == NO_ERROR) {
-        mSensorEventConnection->setEventRate(handle, ms2ns(ms));
+        mSensorEventConnection->setEventRate(handle, us2ns(us));
     }
     return err;
 }