Add a test for field initialization shorthand

tests/source/init_shorthand.rs

@@ -0,0 +1,18 @@
+// Use field initialization shorthand if possible.
+
+fn main() {
+    let a = Foo {
+        x: x,
+        y: y,
+        z: z,
+    };
+
+    let b = Bar {
+        x: x,
+        y: y,
+        #[attr]
+        z: z,
+        #[rustfmt_skip]
+        skipped: skipped,
+    };
+}

tests/target/init_shorthand.rs

@@ -0,0 +1,14 @@
+// Use field initialization shorthand if possible.
+
+fn main() {
+    let a = Foo { x, y, z };
+
+    let b = Bar {
+        x,
+        y,
+        #[attr]
+        z,
+        #[rustfmt_skip]
+        skipped: skipped,
+    };
+}