Update ClipboardService to extend SystemService.

Test: Existing tests still passing.
      cts-tradefed run singleCommand cts-dev --module CtsTextTestCases -t android.text.cts.ClipboardManagerTest
      cts-tradefed run singleCommand cts-dev --module CtsContentTestCases -t android.content.cts.ClipboardManagerTest
      cts-tradefed run singleCommand cts-dev --module CtsDevicePolicyManagerTestCases -t com.android.cts.devicepolicy.ManagedProfileTest#testCrossProfileCopyPaste
Change-Id: Ibca156a412219f11a53f2a9250954b30b650b1aa
diff --git a/services/java/com/android/server/SystemServer.java b/services/java/com/android/server/SystemServer.java
index aba4dc0..6fbe0ff 100644
--- a/services/java/com/android/server/SystemServer.java
+++ b/services/java/com/android/server/SystemServer.java
@@ -859,12 +859,7 @@
 
             if (!disableNonCoreServices) {
                 traceBeginAndSlog("StartClipboardService");
-                try {
-                    ServiceManager.addService(Context.CLIPBOARD_SERVICE,
-                            new ClipboardService(context));
-                } catch (Throwable e) {
-                    reportWtf("starting Clipboard Service", e);
-                }
+                mSystemServiceManager.startService(ClipboardService.class);
                 traceEnd();
             }