Re-implement UserAgent in browser

- Remove calls to SWE's WebSetting API and use the newer implementation of
  the engine. The newer implementation tracks UserAgent per navigation
  entry.
- Allow to override the UserAgent using command line switches.
- Remove debug option to change UserAgent string.
- BrowserConfig class cleanup.

Change-Id: Ib1cc4763e0cbf0207793d1f4e6b1644a9dbb5c08
diff --git a/src/com/android/browser/BrowserPreferencesPage.java b/src/com/android/browser/BrowserPreferencesPage.java
index 09d815e..353a472 100644
--- a/src/com/android/browser/BrowserPreferencesPage.java
+++ b/src/com/android/browser/BrowserPreferencesPage.java
@@ -111,6 +111,7 @@
         "com.android.browser.preferences.LabPreferencesFragment",
         "com.android.browser.preferences.AboutPreferencesFragment",
         "com.android.browser.AutoFillSettingsFragment",
+        "com.android.browser.preferences.DebugPreferencesFragment",
         "com.android.browser.preferences.WebsiteSettingsFragment"));
 
     @Override