Cherry-pick system theme rebase to fix square UI on round watches

Our system themes were based on configurations that were added post-
init of the system theme.

I96e695441543379e4d5fdf3cc6f18d9e6cf953b4 broke this, because there
was a race condition in the code for rebasing themes

If8fecde76d62738a8e55eddf898eafc468afdba2 (the cherry-picked commit)
fixes the race condition and adds the rebasing back in.

This change cherry picks If8fecde76d62738a8e55eddf898eafc468afdba2.

Bug:23387146
Change-Id: I0725028e48599fc6cd9731ae16c71474dd5827e5

services/java/com/android/server/SystemServer.java

@@ -1047,6 +1047,12 @@ public final class SystemServer {
         w.getDefaultDisplay().getMetrics(metrics);
         context.getResources().updateConfiguration(config, metrics);
 
+        // The system context's theme may be configuration-dependent.
+        final Theme systemTheme = context.getTheme();
+        if (systemTheme.getChangingConfigurations() != 0) {
+            systemTheme.rebase();
+        }
+
         try {
             // TODO: use boot phase
             mPowerManagerService.systemReady(mActivityManagerService.getAppOpsService());