Check if anyone could possibly provide service.

If no service is present that could satisfy a given ServiceWatcher,
then return false.  For example, on devices were there is no Geocoder
service implementation, we need to avoid claiming that the API is
supported.

Test: booted
Bug: 30837973
Change-Id: Ib0834cf1a12623733f8b472dc3da7b3e2adc4515

services/core/java/com/android/server/ServiceWatcher.java

@@ -141,8 +141,12 @@ public class ServiceWatcher implements ServiceConnection {
      * <p>
      * Note that if there are no matching encryption-aware services, we may not
      * bind to a real service until after the current user is unlocked.
+     *
+     * @returns {@code true} if a potential service implementation was found.
      */
     public boolean start() {
+        if (isServiceMissing()) return false;
+
         synchronized (mLock) {
             bindBestPackageLocked(mServicePackageName, false);
         }
@@ -173,6 +177,17 @@ public class ServiceWatcher implements ServiceConnection {
         return true;
     }
 
+    /**
+     * Check if any instance of this service is present on the device,
+     * regardless of it being encryption-aware or not.
+     */
+    private boolean isServiceMissing() {
+        final Intent intent = new Intent(mAction);
+        final int flags = PackageManager.MATCH_DIRECT_BOOT_AWARE
+                | PackageManager.MATCH_DIRECT_BOOT_UNAWARE;
+        return mPm.queryIntentServicesAsUser(intent, flags, mCurrentUserId).isEmpty();
+    }
+
     /**
      * Searches and binds to the best package, or do nothing if the best package
      * is already bound, unless force rebinding is requested.
@@ -181,7 +196,7 @@ public class ServiceWatcher implements ServiceConnection {
      *            packages if it is {@code null}.
      * @param forceRebind Force a rebinding to the best package if it's already
      *            bound.
-     * @return {@code true} if a valid package was found to bind to.
+     * @returns {@code true} if a valid package was found to bind to.
      */
     private boolean bindBestPackageLocked(String justCheckThisPackage, boolean forceRebind) {
         Intent intent = new Intent(mAction);