Child storage tests and genesis fix. (#3185)

* Using child storage, (srml-support only), test failing .

* fix simple tests.

* Enumerable by requiring owned struct (previous form only allow
&'static).
Broken tests are from genesis init.

* implement for_child_keys_with_prefix

* indent

* clear_child_prefix fix.

* clear_child_prefix fix 2.

* fix for storage_impl, if/when allowing child and not child this could be
reverted.

* Fix lot of urlinked child genesis, still need to look upon actual
genesis srml module code.
Probably still a lot of broken code needing debugging.

* switch well_known_key to their associated module child trie.
Fix a genesis init (balance).
Complete some testing.
Comment some tests before using.

* fixing test runtime child keys

* latest commit fix broken genesis init

* fix system balances child name.

* Important fix: storage_root from test externalities need children (it is
already the case for ext).

* executive root with child calculation

* Avoid empty trie on test ext.

* Symetric removal of key for system.

* commenting changes related tests.

* Remove child module specifics.

* fix issues.

* fix some formatting

* fix bench and bump runtime

* Remove extend_storage_overlays, assimilate_storage do the same as is
proper considering srml macro.

* Fix warning for assimilate.

* Removing kill as they do not impact any test cases.

* Use tuple of storage map instead of two parameters. This changes the
behavior of decl_storage genesis build closure (breaking api).

* Do not use build storage before assimilate.

* fix error

* Update core/state-machine/src/backend.rs

substrate/core/state-machine/src/lib.rs

@@ -155,15 +155,33 @@ pub trait Externalities<H: Hasher> {
 		self.storage(key).map(|v| H::hash(&v))
 	}
 
+	/// Get child storage value hash. This may be optimized for large values.
+	fn child_storage_hash(&self, storage_key: ChildStorageKey<H>, key: &[u8]) -> Option<H::Out> {
+		self.child_storage(storage_key, key).map(|v| H::hash(&v))
+	}
+
 	/// Read original runtime storage, ignoring any overlayed changes.
 	fn original_storage(&self, key: &[u8]) -> Option<Vec<u8>>;
 
+	/// Read original runtime child storage, ignoring any overlayed changes.
+	fn original_child_storage(&self, storage_key: ChildStorageKey<H>, key: &[u8]) -> Option<Vec<u8>>;
+
 	/// Get original storage value hash, ignoring any overlayed changes.
 	/// This may be optimized for large values.
 	fn original_storage_hash(&self, key: &[u8]) -> Option<H::Out> {
 		self.original_storage(key).map(|v| H::hash(&v))
 	}
 
+	/// Get original child storage value hash, ignoring any overlayed changes.
+	/// This may be optimized for large values.
+	fn original_child_storage_hash(
+		&self,
+		storage_key: ChildStorageKey<H>,
+		key: &[u8],
+	) -> Option<H::Out> {
+		self.original_child_storage(storage_key, key).map(|v| H::hash(&v))
+	}
+
 	/// Read child runtime storage.
 	fn child_storage(&self, storage_key: ChildStorageKey<H>, key: &[u8]) -> Option<Vec<u8>>;
 
@@ -203,6 +221,9 @@ pub trait Externalities<H: Hasher> {
 	/// Clear storage entries which keys are start with the given prefix.
 	fn clear_prefix(&mut self, prefix: &[u8]);
 
+	/// Clear child storage entries which keys are start with the given prefix.
+	fn clear_child_prefix(&mut self, storage_key: ChildStorageKey<H>, prefix: &[u8]);
+
 	/// Set or clear a storage entry (`key`) of current contract being called (effective immediately).
 	fn place_storage(&mut self, key: Vec<u8>, value: Option<Vec<u8>>);