clang-format: [JS] simplify import/export.

Summary:
Change `import` and `export` parsing to special case the renaming
syntax (`import x, {y as bar} ...`, `export {x}`) and otherwise just
parse a regular structural element.

This simplifies the code a bit and should be more correct - it's easier
to recognise the specific import syntax than to recognise arbitrary
expressions and declarations.

Reviewers: djasper

Subscribers: cfe-commits, klimek

Differential Revision: http://reviews.llvm.org/D19242

llvm-svn: 266743
diff --git a/clang/unittests/Format/FormatTestJS.cpp b/clang/unittests/Format/FormatTestJS.cpp
index 5fa91e9..a3cb601 100644
--- a/clang/unittests/Format/FormatTestJS.cpp
+++ b/clang/unittests/Format/FormatTestJS.cpp
@@ -961,6 +961,10 @@
   verifyFormat("export function A() {}\n"
                "export default function B() {}\n"
                "export function C() {}");
+  verifyFormat("export default () => {\n"
+               "  let x = 1;\n"
+               "  return x;\n"
+               "}");
   verifyFormat("export const x = 12;");
   verifyFormat("export default class X {}");
   verifyFormat("export {X, Y} from 'some/module.js';");