new state api state_getKeys to expose storage keys (#1380)

substrate/core/client/db/src/storage_cache.rs

@@ -346,6 +346,10 @@ impl<H: Hasher, S: StateBackend<H>, B:Block> StateBackend<H> for CachingState<H,
 		self.state.pairs()
 	}
 
+	fn keys(&self, prefix: &Vec<u8>) -> Vec<Vec<u8>> {
+		self.state.keys(prefix)
+	}
+
 	fn try_into_trie_backend(self) -> Option<TrieBackend<Self::TrieBackendStorage, H>> {
 		self.state.try_into_trie_backend()
 	}