Fix the Declarative WebRequest API for <webview>

chrome/browser/guest_view/web_view/web_view_constants.cc

Index: chrome/browser/guest_view/web_view/web_view_constants.cc
diff --git a/chrome/browser/guest_view/web_view/web_view_constants.cc b/chrome/browser/guest_view/web_view/web_view_constants.cc
index 68be6a3ed556e9dcfa9d973afcc3475a99439201..1eab8f047bb162a2a7a5c77ddf535356d584b5b4 100644
--- a/chrome/browser/guest_view/web_view/web_view_constants.cc
+++ b/chrome/browser/guest_view/web_view/web_view_constants.cc
@@ -21,6 +21,7 @@ const char kEventLoadProgress[] = "webview.onLoadProgress";
 const char kEventLoadRedirect[] = "webview.onLoadRedirect";
 const char kEventLoadStart[] = "webview.onLoadStart";
 const char kEventLoadStop[] = "webview.onLoadStop";
+const char kEventMessage[] = "webview.onMessage";
 const char kEventNewWindow[] = "webview.onNewWindow";
 const char kEventPermissionRequest[] = "webview.onPermissionRequest";
 const char kEventResponsive[] = "webview.onResponsive";