Renaming didNavigate to continueProgram

There was a TODO to rename didNavigate() to continueProgram upstream. 
As the changes were on both chrome and blink side hence uploading separate patches for the same. 

This patch deals with blink side change.

Link to chromium patch : https://codereview.chromium.org/330663002/

Review URL: https://codereview.chromium.org/330603003

git-svn-id: svn://svn.chromium.org/blink/trunk@176727 bbb929c8-8fbe-4397-9dbb-9b2b20218538