mash: Refactor ChromeLauncherController's ShelfDelegate code.

ash/common/shelf/shelf_delegate.h

Index: ash/common/shelf/shelf_delegate.h
diff --git a/ash/common/shelf/shelf_delegate.h b/ash/common/shelf/shelf_delegate.h
index 6a8d79d42af27ffcfaf9b3f110fbfda2a1d3e85e..dd5ea9156b4619376134e256daaa82be43879e82 100644
--- a/ash/common/shelf/shelf_delegate.h
+++ b/ash/common/shelf/shelf_delegate.h
@@ -30,12 +30,7 @@ class ASH_EXPORT ShelfDelegate {
       const std::string& app_id,
       const std::string& launch_id) = 0;
 
-  // Checks whether a mapping exists from the ShelfID |id| to an app id.
-  virtual bool HasShelfIDToAppIDMapping(ShelfID id) const = 0;
-
   // Get the application ID for a given shelf ID.

[James Cook, 2017/03/23 16:43:49]

nit: What does it return for a bogus/invalid shelf id?

[msw, 2017/03/23 18:08:10]

Documented that this should return an empty string in that case.

-  // |HasShelfIDToAppIDMapping(ShelfID)| should be called first to ensure the
-  // ShelfID can be successfully mapped to an app id.
   virtual const std::string& GetAppIDForShelfID(ShelfID id) = 0;
 
   // Pins an app with |app_id| to shelf. A running instance will get pinned.