GN files for running Closure Compiler

docs/closure_compilation.md

 # Closure Compilation
 
 ## What is type safety?
 
 [Strongly-typed languages](https://en.wikipedia.org/wiki/Strong_and_weak_typing)
 like C++ and Java have the notion of variable types.
 
 This is typically baked into how you declare variables:
 
 ```c++
@@ skipping 64 matching lines @@
 
 ```javascript
 /** @type {number} */ var mensa = wit + 50;
 
 alert(mensa);  // '100 IQ50' instead of 150
 ```
 
 Closure compiler can notify us if we're using `string`s and `number`s in
 dangerous ways.
 
-To do this, we can create:
+To do this, we can create (or add to):
 
-  + ui/compiled_resources2.gyp
+  + ui/BUILD.gn
 
 With these contents:
 
 ```
+
 # Copyright 2016 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
-{
-  'targets': [
-    {
-      # Target names is typically just without ".js"
-      'target_name': 'makes_things_pretty',
+import("//third_party/closure_compiler/compile_js2.gni")
 
-      'dependencies': [
-        '../lib/compiled_resources2.gyp:does_the_hard_stuff',
+# Target name is typically compile_<root file name> but can be anything
+compile_js("compile_make_things_pretty") {
+  source_files = ["make_things_pretty.js"]
+  deps = ["../lib:compile_does_the_hard_stuff"]
+  externs = "extern_name_goes_here"
+}
+...
 
-        # Teaches closure about non-standard environments/APIs, e.g.
-        # chrome.send(), chrome.app.window, etc.
-        '<(EXTERNS_GYP):extern_name_goes_here'
-      ],
+# Create a group to include all compilations in this GN file
+group("compile_js") {
+  deps = [
+    :compile_make_things_pretty,
+    ...
+  ]
+}
 
-      'includes': ['../path/to/third_party/closure_compiler/compile_js2.gypi'],
-    },
-  ],
+```
+
+To include this in builds add your new target to the `'deps'` list in 
+`src/third_party/closure_compiler/BUILD.gn`:
+
+```
+group("compile_js_all") {
+  deps = [
+    # ... other projects ...
+++  "//my_project:compile_js",
+  ]
 }
 ```
 
 ## Running Closure compiler locally
 
 You can locally test that your code compiles on Linux or Mac.  This requires
 [Java](http://www.oracle.com/technetwork/java/javase/downloads/index.html) and a
 [Chrome checkout](http://www.chromium.org/developers/how-tos/get-the-code) (i.e.
 python, depot_tools). Note: on Ubuntu, you can probably just run `sudo apt-get
 install openjdk-7-jre`.
@@ skipping 45 matching lines @@
 To automatically check that your code typechecks cleanly before submitting, you
 can add this line to your CL description:
 
 ```
 CQ_INCLUDE_TRYBOTS=tryserver.chromium.linux:closure_compilation
 ```
 
 Working in common resource directories in Chrome automatically adds this line
 for you.
 
-## Integrating with the continuous build
-
-To compile your code on every commit, add your file to the `'dependencies'` list
-in `src/third_party/closure_compiler/compiled_resources2.gyp`:
-
-```
-{
-  'targets': [
-    {
-      'target_name': 'compile_all_resources',
-      'dependencies': [
-         # ... other projects ...
-++       '../my_project/compiled_resources2.gyp:*',
-      ],
-    }
-  ]
-}
-```
 
 This file is used by the
 [Closure compiler bot](http://build.chromium.org/p/chromium.fyi/builders/Closure%20Compilation%20Linux)
 to automatically compile your code on every commit.