Use AsyncTask when calling Browser.updateVisitedHistory

Previously updateVisitedHistory itself used an AsyncTask, but
since that method could be called from a non-main thread, move
the AsyncTask to the call site.

Part of http://b/issue?id=2539948

Change-Id: I9a70130ab125490fa96964ea9637eba67732180a
diff --git a/src/com/android/browser/Tab.java b/src/com/android/browser/Tab.java
index a5dc975..d450b50 100644
--- a/src/com/android/browser/Tab.java
+++ b/src/com/android/browser/Tab.java
@@ -657,8 +657,14 @@
                     url = url.substring(0, index-1);
                 }
             }
-            Browser.updateVisitedHistory(mActivity.getContentResolver(), url,
-                    true);
+            final ContentResolver cr = mActivity.getContentResolver();
+            final String newUrl = url;
+            new AsyncTask<Void, Void, Void>() {
+                protected Void doInBackground(Void... unused) {
+                    Browser.updateVisitedHistory(cr, newUrl, true);
+                    return null;
+                }
+            }.execute();
             WebIconDatabase.getInstance().retainIconForPageUrl(url);
         }