First pass at experimental omnibox API. There are plenty of rough edges and

chrome/common/extensions/extension.h

Index: chrome/common/extensions/extension.h
diff --git a/chrome/common/extensions/extension.h b/chrome/common/extensions/extension.h
index a135df58dfe268a6c2895f0e8f1eb4e8ba473dfb..49d6288412107355971ad3a571e0846026064524 100644
--- a/chrome/common/extensions/extension.h
+++ b/chrome/common/extensions/extension.h
@@ -327,6 +327,8 @@ class Extension {
     return chrome_url_overrides_;
   }
 
+  const std::string omnibox_keyword() const { return omnibox_keyword_; }
+
   bool web_content_enabled() const { return web_content_enabled_; }
   const ExtensionExtent& web_extent() const { return web_extent_; }
 
@@ -528,6 +530,9 @@ class Extension {
   // resource to the cached image.
   ImageCache image_cache_;
 
+  // The omnibox keyword for this extension, or empty if there is none.
+  std::string omnibox_keyword_;
+
   // Runtime data:
 
   // True if the background page is ready.