Check PendingStartActivityUids in getAppStartModeLocked.

While starting activity, WindowManager posts a runnable to DisplayThread to updateOomAdj.
The UidRecord update could be delayed.

In getAppStartModeLocked(), before checking UidRecord, check PendingStartActivityUids
 to determine if the uid is in foreground state.

Bug: 160213874
Test: Reproduce steps in b/160213874, launch GCA and take a photo immediately.
Change-Id: Ieb984d2f629d607abfbda89ca00f8785cf5923fd

services/core/java/com/android/server/am/ActivityManagerService.java

@@ -6341,6 +6341,9 @@ public class ActivityManagerService extends IActivityManager.Stub
 
     int getAppStartModeLocked(int uid, String packageName, int packageTargetSdk,
             int callingPid, boolean alwaysRestrict, boolean disabledOnly, boolean forcedStandby) {
+        if (mInternal.isPendingTopUid(uid)) {
+            return ActivityManager.APP_START_MODE_NORMAL;
+        }
         UidRecord uidRec = mProcessList.getUidRecordLocked(uid);
         if (DEBUG_BACKGROUND_CHECK) Slog.d(TAG, "checkAllowBackground: uid=" + uid + " pkg="
                 + packageName + " rec=" + uidRec + " always=" + alwaysRestrict + " idle="