Add the main frame routing ID to WebContentsDelegate, use it in BackgroundContents.

content/public/test/content_browser_test.cc

Index: content/public/test/content_browser_test.cc
diff --git a/content/public/test/content_browser_test.cc b/content/public/test/content_browser_test.cc
index fb18659ef53141393ab7d6f6a5571b0109906e9b..395975ad87e27f03fa7e28648797b06f678d5682 100644
--- a/content/public/test/content_browser_test.cc
+++ b/content/public/test/content_browser_test.cc
@@ -161,7 +161,6 @@ Shell* ContentBrowserTest::CreateBrowser() {
       ShellContentBrowserClient::Get()->browser_context(),
       GURL(url::kAboutBlankURL),
       NULL,
-      MSG_ROUTING_NONE,
       gfx::Size());
 }
 
@@ -170,7 +169,6 @@ Shell* ContentBrowserTest::CreateOffTheRecordBrowser() {
       ShellContentBrowserClient::Get()->off_the_record_browser_context(),
       GURL(url::kAboutBlankURL),
       NULL,
-      MSG_ROUTING_NONE,
       gfx::Size());
 }