DO NOT MERGE Restore calling identity before checking permission

Using the system service identity to check the CHANGE_CONFIGURATION
permission isn't likely to catch a security violation. Changing
back to the original caller and then checking permissions is
preferred.

Cherry picked from lmp. Fixes bug 15989465.

Change-Id: Iff08d04422bcc052a487194154f1fd0d727d38f4

services/java/com/android/server/am/ActivityStack.java

@@ -3208,6 +3208,8 @@ final class ActivityStack {
                     aInfo, resultTo, resultWho, requestCode, callingPid, callingUid,
                     callingPackage, startFlags, options, componentSpecified, null);
             
+            Binder.restoreCallingIdentity(origId);
+
             if (mConfigWillChange && mMainStack) {
                 // If the caller also wants to switch to a new configuration,
                 // do so now.  This allows a clean switch, as we are waiting
@@ -3221,8 +3223,6 @@ final class ActivityStack {
                 mService.updateConfigurationLocked(config, null, false, false);
             }
             
-            Binder.restoreCallingIdentity(origId);
-            
             if (outResult != null) {
                 outResult.result = res;
                 if (res == ActivityManager.START_SUCCESS) {