Add support for proxy restrictions

Implement enforcement of the following chromium proxy restrictions:
ProxyMode, ProxyServer, ProxyBypassList

Originally cherry picked from 556a3ba3bb9dae768810181ace1e0b07fd5824c2.

Includes fix for search restriction unit test failures when
including proxy restrictions code.

Also added some logging for functional verification.

Change-Id: If7fc1d8be36fa600a3d974d6b584d504ed2faf71
diff --git a/src/com/android/browser/BrowserSettings.java b/src/com/android/browser/BrowserSettings.java
index b5db3af..ed21c8d 100644
--- a/src/com/android/browser/BrowserSettings.java
+++ b/src/com/android/browser/BrowserSettings.java
@@ -32,6 +32,7 @@
 
 import com.android.browser.R;
 import com.android.browser.homepages.HomeProvider;
+import com.android.browser.mdm.ProxyRestriction;
 import com.android.browser.mdm.SearchEngineRestriction;
 import com.android.browser.platformsupport.Browser;
 import com.android.browser.provider.BrowserProvider;
@@ -133,6 +134,9 @@
         if (mNeedsSharedSync) {
             syncSharedSettings();
         }
+        // Instantiate ProxyRestriction after engine initialization
+        // to ensure ProxyChangeListener is already created.
+        ProxyRestriction.getInstance();
     }
 
     public void startManagingSettings(final WebSettings settings) {