pkg/docgen: putting test code in file system

pkg/docgen/test/multi_library_code/lib/temp.dart

+library testLib;
+import 'temp2.dart';
+import 'temp3.dart';
+export 'temp2.dart';
+export 'temp3.dart';
+
+/**
+ * Doc comment for class [A].
+ *
+ * Multiline Test
+ */
+/*
+ * Normal comment for class A.
+ */
+class A {
+
+  int _someNumber;
+
+  A() {
+    _someNumber = 12;
+  }
+
+  A.customConstructor();
+
+  /**
+   * Test for linking to parameter [A]
+   */
+  void doThis(int A) {
+    print(A);
+  }
+}
+
+// A trivial use of `B` and `C` to eliminate import warnings
+B sampleMethod(C cInstance) {
+  throw new UnimplementedError();
+}