Add a flag that lets the webstore show a different UI on app install.

chrome/common/chrome_switches.cc

Index: chrome/common/chrome_switches.cc
diff --git a/chrome/common/chrome_switches.cc b/chrome/common/chrome_switches.cc
index 5f6ec9eb257211f02df011a2a72550fad3ee48e4..afaf93a496f6c9f04f85eb2d4942184ff6a61ecf 100644
--- a/chrome/common/chrome_switches.cc
+++ b/chrome/common/chrome_switches.cc
@@ -70,6 +70,9 @@ const char kAppsGalleryURL[]                = "apps-gallery-url";
 // The update url used by gallery/webstore extensions.
 const char kAppsGalleryUpdateURL[]          = "apps-gallery-update-url";
 
+// Whether to always use the new app install bubble when installing an app.
+const char kAppsNewInstallBubble[]          = "apps-new-install-bubble";
+
 // Disable throbber for extension apps.
 const char kAppsNoThrob[]                   = "apps-no-throb";