Minimize uses of lazy initialization by adding explicit initialization functions.

src/lazy-instance.h

Index: src/lazy-instance.h
diff --git a/src/lazy-instance.h b/src/lazy-instance.h
index 4beb55c0a291b05cf91bde23ffd8af03f1be9f6a..5bbe230fb6d85d382348c241d32ac232d96d6378 100644
--- a/src/lazy-instance.h
+++ b/src/lazy-instance.h
@@ -65,8 +65,12 @@
 //   static LazyInstance<MyClass, MyCreateTrait>::type my_instance =
 //      LAZY_INSTANCE_INITIALIZER;
 //
-// WARNING: This implementation of LazyInstance is NOT thread-safe by default.
-// See ThreadSafeInitOnceTrait declared below for that.
+// WARNINGS:
+// - This implementation of LazyInstance is NOT THREAD-SAFE by default. See
+//   ThreadSafeInitOnceTrait declared below for that.
+// - Lazy initialization comes with a cost. Make sure that you don't use it on
+//   critical path. Consider adding your initialization code to a function
+//   which is explicitly called once.
 //
 // Notes for advanced users:
 // LazyInstance can actually be used in two different ways: