Merge branch 'fix-flow-optional-type' of https://github.com/danez/babylon into danez-fix-flow-optional-type

# Conflicts:
#	src/plugins/flow.js

src/plugins/flow.js

@@ -726,9 +726,29 @@ export default function (instance) {
     };
   });
 
+  instance.extend("parseConditional", function (inner) {
+    return function (expr, noIn, startPos, startLoc, refNeedsArrowPos) {
+      const state = this.state.clone();
+      try {
+        return inner.call(this, expr, noIn, startPos, startLoc);
+      } catch (err) {
+        if (refNeedsArrowPos && err instanceof SyntaxError) {
+          this.state = state;
+          refNeedsArrowPos.start = this.state.start;
+          return expr;
+        } else {
+          throw err;
+        }
+      }
+    };
+  });
+
   instance.extend("parseParenItem", function (inner) {
     return function (node, startLoc, startPos) {
       node = inner.call(this, node, startLoc, startPos);
+      if (this.eat(tt.question)) {
+        node.optional = true;
+      }
 
       if (this.match(tt.colon)) {
         let typeCastNode = this.startNodeAt(startLoc, startPos);