Weight annotation for block hooks. (#4058)

* Initial version that works with proper tests.

* get rid of todos and grumbles and such.

* Cleanup and fix line-width

* fix test runtime test

substrate/srml/example/src/lib.rs

@@ -498,13 +498,18 @@ decl_module! {
 			<Dummy<T>>::put(new_value);
 		}
 
-		// The signature could also look like: `fn on_initialize()`
+		// The signature could also look like: `fn on_initialize()`.
+		// This function could also very well have a weight annotation, similar to any other. The
+		// only difference being that if it is not annotated, the default is
+		// `SimpleDispatchInfo::zero()`, which resolves into no weight.
+		#[weight = SimpleDispatchInfo::FixedNormal(1000)]
 		fn on_initialize(_n: T::BlockNumber) {
 			// Anything that needs to be done at the start of the block.
 			// We don't do anything here.
 		}
 
 		// The signature could also look like: `fn on_finalize()`
+		#[weight = SimpleDispatchInfo::FixedNormal(2000)]
 		fn on_finalize(_n: T::BlockNumber) {
 			// Anything that needs to be done at the end of the block.
 			// We just kill our dummy storage item.