Ensure arrow function bodies are wrapped in parens if needed.

Closes #1214.

src/babel/generation/generators/methods.js

@@ -75,5 +75,16 @@ export function ArrowFunctionExpression(node, print) {
   }
 
   this.push(" => ");
+
+  const bodyNeedsParens = t.isObjectExpression(node.body);
+
+  if (bodyNeedsParens) {
+    this.push("(");
+  }
+
   print(node.body);
+
+  if (bodyNeedsParens) {
+    this.push(")");
+  }
 }

test/core/fixtures/generation/parentheses/arrow-function-object-body/actual.js

@@ -0,0 +1,4 @@
+var foo = arr.map(v => ({
+  x: v.bar,
+  y: v.bar*2
+}));

test/core/fixtures/generation/parentheses/arrow-function-object-body/expected.js

@@ -0,0 +1,4 @@
+var foo = arr.map(v => ({
+  x: v.bar,
+  y: v.bar * 2
+}));