Revert of Do not trigger new history entry if iframe URL doesn't change (https://codereview.chromium.org/201773002/)

Reason for revert:
This may have broken browser_tests: http://build.chromium.org/p/chromium.webkit/builders/Linux%20Tests%20%28dbg%29/builds/2034/steps/browser_tests/logs/TabDestroyed

Original issue's description:
> Do not trigger new history entry if iframe URL doesn't change
> 
> When URL of an iframe changes from "unset" to "set", we don't want to
> create new history entry. This worked for URLs without fragment
> identifier but failed with it present.
> 
> This change takes the idea from the old code, before it was rewritten
> in https://codereview.chromium.org/126453005
> 
> BUG=353096
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=169665

TBR=abarth@chromium.org,japhet@chromium.org,rchlodnicki@opera.com
NOTREECHECKS=true
NOTRY=true
BUG=353096

Review URL: https://codereview.chromium.org/207683003

git-svn-id: svn://svn.chromium.org/blink/trunk@169723 bbb929c8-8fbe-4397-9dbb-9b2b20218538