gn: Mention loadable_module targets in the cookbook.

loadable_modules are quite commonly used in tests and for plugins, yet
it is barely mentioned in GN's docs.

Add it to the cookbook so people porting their projects away from gyp
know that the construct also exists in GN.

R=brettw@chromium.org,dpranke@chromium.org

Review-Url: https://codereview.chromium.org/2276943005
Cr-Original-Commit-Position: refs/heads/master@{#414458}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 11772ab50084dc52be85d02064148fbf57e0ae15

tools/gn/docs/cookbook.md

diff --git a/tools/gn/docs/cookbook.md b/tools/gn/docs/cookbook.md
index 7f02e13..0065b99 100644
--- a/tools/gn/docs/cookbook.md
+++ b/tools/gn/docs/cookbook.md
@@ -8,6 +8,7 @@
 |:-------------------------------------------------|:---------------------------------------------------|
 | `'type': 'static_library', 'name': 'foo',`       | `static_library("foo") {` or `source_set("foo") {` |
 | `'type': 'shared_library', 'name': 'foo',`       | `shared_library("foo") {`                          |
+| `'type': 'loadable_module', 'name': 'foo',`      | `loadable_module("foo") {`                         |
 | `'type': '<(component)', 'name': 'foo',`         | `component("foo") {`                               |
 | `'type': 'executable', 'name': 'foo',`           | `executable("foo") {`                              |
 | `'type': '<(gtest_target_type)', 'name': 'foo',` | `test("foo") {`                                    |