Add WebstoreInlineInstaller (downloads store data, shows the install UI, and starts the install).

chrome/common/extensions/extension_constants.h

Index: chrome/common/extensions/extension_constants.h
diff --git a/chrome/common/extensions/extension_constants.h b/chrome/common/extensions/extension_constants.h
index 925b38f948e4fa6d5b405a36258efa2a0217cf61..ba14dd5d1262ff758b7a09fbb77d866de4d1c0b1 100644
--- a/chrome/common/extensions/extension_constants.h
+++ b/chrome/common/extensions/extension_constants.h
@@ -281,6 +281,10 @@ namespace extension_urls {
   // to get the item detail URL.
   std::string GetWebstoreItemDetailURLPrefix();
 
+  // Returns the URL used to get webstore data (ratings, manifest, icon URL,
+  // etc.) about an extension from the webstore as JSON.
+  GURL GetWebstoreItemJsonDataURL(const std::string& extension_id);
+
   // Return the update URL used by gallery/webstore extensions/apps. The
   // |secure| parameter will be ignored if the update URL is overriden with
   // --apps-gallery-update-url.