Add support for this type to Babel 6.x

packages/babel-generator/src/generators/flow.js

@@ -140,6 +140,10 @@ export function StringTypeAnnotation() {
   this.push("string");
 }
 
+export function ThisTypeAnnotation() {
+  this.push("this");
+}
+
 export function TupleTypeAnnotation(node: Object) {
   this.push("[");
   this.printJoin(node.types, node, { separator: ", " });

packages/babel-generator/test/fixtures/flow/this-types/actual.js

@@ -0,0 +1,5 @@
+class Foo {
+  bar(): this {
+    return this;
+  }
+}

packages/babel-generator/test/fixtures/flow/this-types/expected.js

@@ -0,0 +1,5 @@
+class Foo {
+  bar(): this {
+    return this;
+  }
+}