Show an opaque background if showing the new user search engine promo.

chrome/android/java/src/org/chromium/chrome/browser/widget/PromoDialog.java

Index: chrome/android/java/src/org/chromium/chrome/browser/widget/PromoDialog.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/widget/PromoDialog.java b/chrome/android/java/src/org/chromium/chrome/browser/widget/PromoDialog.java
index 30626367d2d2b085d6c12865232360c7e58914a9..502b33aeef1e05774d4cdc96916a209131710d6b 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/widget/PromoDialog.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/widget/PromoDialog.java
@@ -6,6 +6,10 @@ package org.chromium.chrome.browser.widget;
 
 import android.app.Activity;
 import android.content.DialogInterface;
+import android.graphics.Color;
+import android.graphics.drawable.ColorDrawable;
+import android.graphics.drawable.Drawable;
+import android.graphics.drawable.LayerDrawable;
 import android.os.Bundle;
 import android.view.LayoutInflater;
 import android.view.View;
@@ -67,6 +71,17 @@ public abstract class PromoDialog extends AlwaysDismissedDialog
         mDialogLayout.initialize(getDialogParams());
     }
 
+    /**
+     * Force the promo dialog to have a fully opaque background hiding any underlying content.
+     */
+    protected void forceOpaqueBackground() {
+        LayerDrawable background = new LayerDrawable(new Drawable[] {
+                new ColorDrawable(Color.WHITE),
+                new ColorDrawable(ApiCompatibilityUtils.getColor(
+                        getContext().getResources(), R.color.modal_dialog_scrim_color))});
+        mScrimView.setBackground(background);
+    }
+
     /**
      * Adds a View to the layout within the scrollable area.
      * See {@link PromoDialogLayout#addControl}.