Allow only responsive websites to install as a web app on mobile.

chrome/browser/banners/app_banner_debug_log.cc

Index: chrome/browser/banners/app_banner_debug_log.cc
diff --git a/chrome/browser/banners/app_banner_debug_log.cc b/chrome/browser/banners/app_banner_debug_log.cc
index 36818b0b6ade365ccece596be18304a58e9c7375..67bfe21b482cf37b9e3206c2ee80b31ba5b97cd8 100644
--- a/chrome/browser/banners/app_banner_debug_log.cc
+++ b/chrome/browser/banners/app_banner_debug_log.cc
@@ -39,6 +39,11 @@ const char kNotServedFromSecureOrigin[] =
 const char kIgnoredNotSupportedOnAndroid[] =
     " application ignored: not supported on Android";
 const char kIgnoredNoId[] = "play application ignored: no id provided";
+const char kMetaViewportTagError[] =
+    "meta viewport tag not detected, or it contains no indication that your "
+    "site scales for mobile devices. Please check that your site displays "
+    "appropriately on mobile, and add the meta viewport tag with content "
+    "width=device-width or initial-scale=1";
 
 void OutputDeveloperNotShownMessage(content::WebContents* web_contents,
                                     const std::string& message) {