Only register stationary detector while idle

The stationary detector takes some non-zero amount of power, this
should help save power in the case where the device is not idle.

Bug: 196997374
Test: manual + presubmit
Change-Id: Ia1f0b85ee5ccb8a61b3f4514ccbeaf1eef36016b

services/core/java/com/android/server/location/provider/StationaryThrottlingLocationProvider.java

@@ -105,20 +105,15 @@ public final class StationaryThrottlingLocationProvider extends DelegateLocation
 
         synchronized (mLock) {
             mDeviceIdleHelper.addListener(this);
-            mDeviceIdle = mDeviceIdleHelper.isDeviceIdle();
-            mDeviceStationaryHelper.addListener(this);
-            mDeviceStationary = false;
-            mDeviceStationaryRealtimeMs = Long.MIN_VALUE;
-
-            onThrottlingChangedLocked(false);
+            onDeviceIdleChanged(mDeviceIdleHelper.isDeviceIdle());
         }
     }
 
     @Override
     protected void onStop() {
         synchronized (mLock) {
-            mDeviceStationaryHelper.removeListener(this);
             mDeviceIdleHelper.removeListener(this);
+            onDeviceIdleChanged(false);
 
             mIncomingRequest = ProviderRequest.EMPTY_REQUEST;
             mOutgoingRequest = ProviderRequest.EMPTY_REQUEST;
@@ -151,13 +146,26 @@ public final class StationaryThrottlingLocationProvider extends DelegateLocation
             }
 
             mDeviceIdle = deviceIdle;
-            onThrottlingChangedLocked(false);
+
+            if (deviceIdle) {
+                // device stationary helper will deliver an immediate listener update
+                mDeviceStationaryHelper.addListener(this);
+            } else {
+                mDeviceStationaryHelper.removeListener(this);
+                mDeviceStationary = false;
+                mDeviceStationaryRealtimeMs = Long.MIN_VALUE;
+            }
         }
     }
 
     @Override
     public void onDeviceStationaryChanged(boolean deviceStationary) {
         synchronized (mLock) {
+            if (!mDeviceIdle) {
+                // stationary detection is only registered while idle - ignore late notifications
+                return;
+            }
+
             if (mDeviceStationary == deviceStationary) {
                 return;
             }