Credential Manager: Add the API to about:flags.

chrome/app/generated_resources.grd

Index: chrome/app/generated_resources.grd
diff --git a/chrome/app/generated_resources.grd b/chrome/app/generated_resources.grd
index aa67dac88fd94b37ea5ea31340888e3f831a58bf..fcbdb4b00d5dadb30c4cdbb572f183da2d898004 100644
--- a/chrome/app/generated_resources.grd
+++ b/chrome/app/generated_resources.grd
@@ -6094,6 +6094,12 @@ Keep your key file in a safe place. You will need it to create new versions of y
       <message name="IDS_FLAGS_ENABLE_VIEWPORT_META_DESCRIPTION" desc="Description of the flag to turn on viewport meta tag support.">
         Enables handling of the viewport meta tag to allow pages to set the layout width and user zoom properties.
       </message>
+      <message name="IDS_FLAGS_CREDENTIAL_MANAGER_API_NAME" desc="Name for the flag to enable 'navigator.credentials'.">
+        Enable the experimental Credential Manager API.
+      </message>
+      <message name="IDS_FLAGS_CREDENTIAL_MANAGER_API_DESCRIPTION" desc="Description for the flag to enable 'navigator.credentials'.">
+        Enables an experimental implementation of the Credential Manager API. No promises that this won't expose all your passwords to every site on the web; don't enable this unless you know what you're doing.
+      </message>
 
       <if expr="chromeos">
         <message name="IDS_FLAGS_ALLOW_TOUCHPAD_THREE_FINGER_CLICK_NAME" desc="Name for the flag to enable touchpad three finger click as middle button.">