Allow extension APIs to be called from WebUI.

extensions/common/api/_api_features.json

 // Copyright 2014 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.
 
 // This features file defines extension APIs implemented under src/extensions.
 // See extensions/common/features/* to understand this file, in particular
 // feature.h, simple_feature.h, and base_feature_provider.h.
 //
 // Note that specifying "web_page", "blessed_web_page", or "all" as a context
 // type will require manually updating chrome/renderer/resources/dispatcher.cc.
@@ skipping 35 matching lines @@
   },
   "runtime": {
     "channel": "stable",
     "extension_types": ["extension", "legacy_packaged_app", "platform_app"],
     "contexts": ["blessed_extension"]
   },
   "runtime.getManifest": {
     "contexts": ["blessed_extension", "unblessed_extension", "content_script"]
   },
   "runtime.connect": {
-    "contexts": "all",
+    // Everything except WebUI.
+    "contexts": [
+      "blessed_web_page",
+      "content_script",
+      "blessed_extension",
+      "unblessed_extension",
+      "web_page"
+    ],
     "matches": ["<all_urls>"]
   },
   "runtime.getURL": {
     "contexts": ["blessed_extension", "unblessed_extension", "content_script"]
   },
   "runtime.id": {
     "contexts": ["blessed_extension", "unblessed_extension", "content_script"]
   },
   "runtime.lastError": {
     "contexts": "all",
     "extension_types": "all",
     "matches": ["<all_urls>"]
   },
   "runtime.onConnect": {
     "contexts": ["blessed_extension", "unblessed_extension", "content_script"]
   },
   "runtime.onMessage": {
     "contexts": ["blessed_extension", "unblessed_extension", "content_script"]
   },
   "runtime.sendMessage": {
-    "contexts": "all",
+    // Everything except WebUI.
+    "contexts": [
+      "blessed_web_page",
+      "content_script",
+      "blessed_extension",
+      "unblessed_extension",
+      "web_page"
+    ],
     "matches": ["<all_urls>"]
   },
   "runtime.setUninstallURL": {
     "channel": "dev"
   },
   "socket": {
     "dependencies": ["permission:socket"],
     "contexts": ["blessed_extension"]
   },
   "sockets.tcp": {
     "dependencies": ["manifest:sockets"],
     "contexts": ["blessed_extension"]
   },
   "sockets.tcpServer": {
     "dependencies": ["manifest:sockets"],
     "contexts": ["blessed_extension"]
   },
   "sockets.udp": {
     "dependencies": ["manifest:sockets"],
     "contexts": ["blessed_extension"]
   },
   "storage": {
     "dependencies": ["permission:storage"],
     "contexts": ["blessed_extension", "unblessed_extension", "content_script"]
   },
   "test": {
     "internal": true,
     "channel": "stable",
     "extension_types": "all",
-    "contexts": ["blessed_extension", "unblessed_extension", "content_script"]
+    // Everything except web pages.
+    "contexts": [
+      "blessed_extension",
+      "content_script",
+      "unblessed_extension",
+      "webui"
+    ]
   },
   "types": {
     "channel": "stable",
     "extension_types": ["extension", "legacy_packaged_app", "platform_app"],
     "contexts": ["blessed_extension"]
   },
   "types.private": {
     "channel": "dev",
     "extension_types": ["extension"],
     "location": "component"
   },
   "usb": {
     "dependencies": ["permission:usb"],
     "contexts": ["blessed_extension"]
   }
 }