godoc: hide appengine dependencies behind build tags

Fixes the continuous build.

Change-Id: If55b08c3b702ba705d84a30fdbce842438477883
Reviewed-on: https://go-review.googlesource.com/18241
Reviewed-by: Andrew Gerrand <adg@golang.org>

godoc/dl/dl.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by the Apache 2.0
 // license that can be found in the LICENSE file.
 
+// +build appengine
+
 // Package dl implements a simple downloads frontend server.
 //
 // It accepts HTTP POST requests to create a new download metadata entity, and

godoc/dl/dl_test.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by the Apache 2.0
 // license that can be found in the LICENSE file.
 
+// +build appengine
+
 package dl
 
 import (

godoc/dl/tmpl.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by the Apache 2.0
 // license that can be found in the LICENSE file.
 
+// +build appengine
+
 package dl
 
 // TODO(adg): refactor this to use the tools/godoc/static template.

godoc/proxy/appengine.go

@@ -1,13 +0,0 @@
-// Copyright 2015 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.
-
-// +build appengine
-
-package proxy
-
-import "google.golang.org/appengine"
-
-func init() {
-	onAppengine = !appengine.IsDevAppServer()
-}

godoc/proxy/proxy.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build appengine
+
 // Package proxy proxies requests to the sandbox compiler service and the
 // playground share handler.
 // It is designed to run only on the instance of godoc that serves golang.org.
@@ -155,10 +157,8 @@ func share(w http.ResponseWriter, r *http.Request) {
 	p.ServeHTTP(w, r)
 }
 
-var onAppengine = false // will be overriden by appengine.go and appenginevm.go
-
 func allowShare(r *http.Request) bool {
-	if !onAppengine {
+	if appengine.IsDevAppServer() {
 		return true
 	}
 	switch r.Header.Get("X-AppEngine-Country") {

godoc/short/short.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by the Apache 2.0
 // license that can be found in the LICENSE file.
 
+// +build appengine
+
 // Package short implements a simple URL shortener, serving an administrative
 // interface at /s and shortened urls from /s/key.
 // It is designed to run only on the instance of godoc that serves golang.org.

godoc/short/tmpl.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by the Apache 2.0
 // license that can be found in the LICENSE file.
 
+// +build appengine
+
 package short
 
 const templateHTML = `