Allow extension APIs to be called from WebUI.

extensions/common/api/_api_features.json

Index: extensions/common/api/_api_features.json
diff --git a/extensions/common/api/_api_features.json b/extensions/common/api/_api_features.json
index 2052a41412364ae1a5304c8b018ab0e5ed129c9d..e15c27b618df13991516270b15184bfb742ac9b6 100644
--- a/extensions/common/api/_api_features.json
+++ b/extensions/common/api/_api_features.json
@@ -53,7 +53,14 @@
     "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": {
@@ -74,7 +81,14 @@
     "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": {
@@ -104,7 +118,13 @@
     "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",