Add a unit test for the experimental app list.

ui/app_list/views/start_page_view.cc

Index: ui/app_list/views/start_page_view.cc
diff --git a/ui/app_list/views/start_page_view.cc b/ui/app_list/views/start_page_view.cc
index e1c0e2f40538521edc6a71f6b49ddc63a214d37c..164cee1a58fa59aba9eb2d0864fa07dcb83983e0 100644
--- a/ui/app_list/views/start_page_view.cc
+++ b/ui/app_list/views/start_page_view.cc
@@ -72,8 +72,9 @@ StartPageView::StartPageView(AppListMainView* app_list_main_view,
   instant_container_->SetLayoutManager(new views::BoxLayout(
       views::BoxLayout::kVertical, 0, kTopMargin, kInstantContainerSpacing));
 
-  views::WebView* web_view =
-      new views::WebView(start_page_web_contents->GetBrowserContext());
+  views::WebView* web_view = new views::WebView(
+      start_page_web_contents ? start_page_web_contents->GetBrowserContext()
+                              : NULL);
   web_view->SetPreferredSize(gfx::Size(kWebViewWidth, kWebViewHeight));
   web_view->SetWebContents(start_page_web_contents);