Method names should not be bound to body

As an artificat of compiling methods to named function expressions the
function name is being considered a "local" binding in the function
body. This means that we will throw errors anytime someone would want to
create a new local binding with the same name.

This is solved by assigning a symbol to function Identifiers that
indicates that they should not be considered local bindings.

packages/babel-helper-define-map/src/index.js

@@ -63,6 +63,11 @@ export function push(mutatorMap: Object, node: Object, kind: string, file, scope
   // infer function name
   if (scope && t.isStringLiteral(key) && (kind === "value" || kind === "initializer") && t.isFunctionExpression(value)) {
     value = nameFunction({ id: key, node: value, scope });
+
+    // Class methods don't have their name bound in the funciton body.
+    if (t.isClassMethod(node)) {
+      value.id[t.NOT_LOCAL_BINDING] = true
+    }
   }
 
   if (value) {