<webview>: Partially migrate loadcommit event from content to chrome

chrome/browser/webview/webview_constants.h

Index: chrome/browser/webview/webview_constants.h
diff --git a/chrome/browser/webview/webview_constants.h b/chrome/browser/webview/webview_constants.h
index ee8cef478403dbaf0425b71da41f02640354792f..d796555d7ff80e8811fa0072b98c3bc49633fc7c 100644
--- a/chrome/browser/webview/webview_constants.h
+++ b/chrome/browser/webview/webview_constants.h
@@ -9,6 +9,13 @@
 
 namespace webview_constants {
 
+// Events.
+extern const char kEventLoadCommit[];
+
+// Parameters/properties on events.
+extern const char kIsTopLevel[];
+extern const char kUrl[];
+
 // Attributes.
 extern const char kAttributeApi[];