Split web_view_internal_api and move part of it to extensions.

extensions/browser/guest_view/web_view/web_view_constants.cc

Index: extensions/browser/guest_view/web_view/web_view_constants.cc
diff --git a/extensions/browser/guest_view/web_view/web_view_constants.cc b/extensions/browser/guest_view/web_view/web_view_constants.cc
index fd028c1e5b1f52b957ece173c8a6713feff3d029..4e2ee9055f02836fb8f2da96da31087572869943 100644
--- a/extensions/browser/guest_view/web_view/web_view_constants.cc
+++ b/extensions/browser/guest_view/web_view/web_view_constants.cc
@@ -20,7 +20,7 @@ const char kAPINamespace[] = "webViewInternal";
 const char kEventClose[] = "webViewInternal.onClose";
 const char kEventConsoleMessage[] = "webViewInternal.onConsoleMessage";
 const char kEventContentLoad[] = "webViewInternal.onContentLoad";
-const char kEventContextMenu[] = "webViewInternal.contextmenu";
+const char kEventContextMenu[] = "chromeWebViewInternal.contextmenu";
 const char kEventDialog[] = "webViewInternal.onDialog";
 const char kEventExit[] = "webViewInternal.onExit";
 const char kEventFindReply[] = "webViewInternal.onFindReply";