Use the externally_connectable schema from manifest_types.json to generate its

chrome/common/extensions/api/manifest_types.json

Index: chrome/common/extensions/api/manifest_types.json
diff --git a/chrome/common/extensions/api/manifest_types.json b/chrome/common/extensions/api/manifest_types.json
index 1fa069bf695945c61f719d02a18c2c4295c48bc0..e14ed37969f5e49cc937a833fb5f93ff7287ccf3 100644
--- a/chrome/common/extensions/api/manifest_types.json
+++ b/chrome/common/extensions/api/manifest_types.json
@@ -3,7 +3,6 @@
 // found in the LICENSE file.
 
 // The type schemas for structured manifest items. Not actually a callable API.
-// TODO(kalman): Expose these in the docs somewhere.
 
 [
   {
@@ -16,16 +15,18 @@
       {
         "id": "ExternallyConnectable",
         "type": "object",
-        "description": "The schema of the <code>externally_connectable</code> manifest property",
+        // Note: description commented out because externally_connectable.html
+        // already describes it, and the repetition looks odd.
+        // "description": "The <code>externally_connectable</code> manifest property declares which extensions, apps, and web pages can connect to your extension via $ref:runtime.connect and $ref:runtime.sendMessage.",
         "properties": {
-          "matches": {
-            "description": "<p>The URL patterns for web pages that are allowed to connect. If left empty or unspecified, no web pages can connect.</p><p>Patterns cannot include wildcard domains nor subdomains of (effective) top level domains; <code>*://google.com/*</code> and <code>http://*.chromium.org/*</code> are valid, while <code>&lt;all_urls&gt;</code>, <code>http://*/*</code>, <code>*://*.com/*</code>, and even <code>http://*.appspot.com/*</code> are not.</p>",
+          "ids": {
+            "description": "<p>The IDs of extensions or apps that are allowed to connect. If left empty or unspecified, no extensions or apps can connect.</p><p>The wildcard <code>\"*\"</code> will allow all extensions and apps to connect.</p>",
             "optional": true,
             "type": "array",
             "items": {"type": "string"}
           },
-          "ids": {
-            "description": "The IDs of extensions or apps that are allowed to connect. If left empty or unspecified, no extensions nor apps can connect. <code>*</code> will match all extension and app IDs.",
+          "matches": {
+            "description": "<p>The URL patterns for <em>web pages</em> that are allowed to connect. <em>This does not affect content scripts.</em> If left empty or unspecified, no web pages can connect.</p><p>Patterns cannot include wildcard domains nor subdomains of (effective) top level domains; <code>*://google.com/*</code> and <code>http://*.chromium.org/*</code> are valid, while <code>&lt;all_urls&gt;</code>, <code>http://*/*</code>, <code>*://*.com/*</code>, and even <code>http://*.appspot.com/*</code> are not.</p>",
             "optional": true,
             "type": "array",
             "items": {"type": "string"}