Add a handler for enabled/disabling assist.

chrome/android/java/src/org/chromium/chrome/browser/ChromeActivity.java

Index: chrome/android/java/src/org/chromium/chrome/browser/ChromeActivity.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/ChromeActivity.java b/chrome/android/java/src/org/chromium/chrome/browser/ChromeActivity.java
index 3859e8cd0a95f54c7d7a6cafb7901eef04e4c7a7..e1956408fa8b5af7e269c6b36350c70a99c98e91 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/ChromeActivity.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/ChromeActivity.java
@@ -210,6 +210,8 @@ public abstract class ChromeActivity extends AsyncInitializationActivity
 
     private final Locale mCurrentLocale = Locale.getDefault();
 
+    private AssistStatusHandler mAssistStatusHandler;
+
     private static AppMenuHandlerFactory sAppMenuHandlerFactory = new AppMenuHandlerFactory() {
         @Override
         public AppMenuHandler get(
@@ -245,6 +247,14 @@ public abstract class ChromeActivity extends AsyncInitializationActivity
         mSnackbarManager = new SnackbarManager(getWindow());
         mLoFiBarPopupController = new LoFiBarPopupController(this, getSnackbarManager());
 
+        mAssistStatusHandler = createAssistStatusHandler();
+        if (mAssistStatusHandler != null) {
+            if (mTabModelSelector != null) {
+                mAssistStatusHandler.setTabModelSelector(mTabModelSelector);
+            }
+            mAssistStatusHandler.updateAssistState();
+        }
+
         // Low end device UI should be allowed only after a fresh install or when the data has
         // been cleared. This must happen before anyone calls SysUtils.isLowEndDevice() or
         // SysUtils.isLowEndDevice() will always return the wrong value.
@@ -384,6 +394,20 @@ public abstract class ChromeActivity extends AsyncInitializationActivity
     }
 
     /**
+     * @return The assist handler for this activity.
+     */
+    protected AssistStatusHandler getAssistStatusHandler() {
+        return mAssistStatusHandler;
+    }
+
+    /**
+     * @return A newly constructed assist handler for this given activity type.
+     */
+    protected AssistStatusHandler createAssistStatusHandler() {
+        return new AssistStatusHandler(this);
+    }
+
+    /**
      * @return The resource id for the layout to use for {@link ControlContainer}. 0 by default.
      */
     protected int getControlContainerLayoutId() {
@@ -482,6 +506,10 @@ public abstract class ChromeActivity extends AsyncInitializationActivity
                 postDeferredStartupIfNeeded();
             }
         };
+
+        if (mAssistStatusHandler != null) {
+            mAssistStatusHandler.setTabModelSelector(tabModelSelector);
+        }
     }
 
     @Override