go/parser: example for ParseFile use

R=r
CC=golang-dev
https://golang.org/cl/5675074

src/pkg/go/parser/example_test.go

+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package parser_test
+
+import (
+	"fmt"
+	"go/parser"
+	"go/token"
+)
+
+func ExampleParseFile() {
+	fset := token.NewFileSet() // positions are relative to fset
+
+	// Parse the file containing this very example
+	// but stop after processing the imports.
+	f, err := parser.ParseFile(fset, "example_test.go", nil, parser.ImportsOnly)
+	if err != nil {
+		fmt.Println(err)
+		return
+	}
+
+	// Print the imports from the file's AST.
+	for _, s := range f.Imports {
+		fmt.Println(s.Path.Value)
+	}
+
+	// output:
+	//
+	// "fmt"
+	// "go/parser"
+	// "go/token"
+}