Push API: use an enum to indicate status.

content/shell/renderer/test_runner/mock_web_push_client.cc

Index: content/shell/renderer/test_runner/mock_web_push_client.cc
diff --git a/content/shell/renderer/test_runner/mock_web_push_client.cc b/content/shell/renderer/test_runner/mock_web_push_client.cc
index 5b846c3e01ff0392b75d5bf8e93040cce6aa8aff..efb13838eab27cb549661383ae70a1d9c4f0c164 100644
--- a/content/shell/renderer/test_runner/mock_web_push_client.cc
+++ b/content/shell/renderer/test_runner/mock_web_push_client.cc
@@ -15,9 +15,8 @@ using blink::WebString;
 namespace content {
 
 MockWebPushClient::MockWebPushClient()
-  // The default state should be be an error with "Registration failed." message
-  // because LayoutTests are currently depending on that.
-  : error_message_("Registration failed.") {
+    : error_message_(
+          "Registration failed (default mock client error message)") {
 }
 
 MockWebPushClient::~MockWebPushClient() {}