[iframe] Move tests to the own directory

From `css/css-sizing` to `css/css-sizing/responsive-iframe`.

Bug: 418397278
Change-Id: I06c1c92b8d50ad4a42380cbea29326ab262829d6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7048179
Commit-Queue: Koji Ishii <kojii@chromium.org>
Reviewed-by: Koji Ishii <kojii@chromium.org>
Reviewed-by: Kent Tamura <tkent@chromium.org>
Auto-Submit: Koji Ishii <kojii@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1531200}

Author: kojiishi

css/css-sizing/resources/iframe-contents-request-resize.html renamed to css/css-sizing/responsive-iframe/resources/iframe-contents-request-resize.html

@@ -8,5 +8,5 @@
     border: 1px solid black;
 }
 </style>
-<iframe frameborder=0 scrolling=no src="http://{{hosts[alt][]}}:{{ports[http][0]}}/css/css-sizing/resources/iframe-contents.html">
+<iframe frameborder=0 scrolling=no src="http://{{hosts[alt][]}}:{{ports[http][0]}}/css/css-sizing/responsive-iframe/resources/iframe-contents.html">
 </iframe>

css/css-sizing/resources/iframe-contents-unsized.html renamed to css/css-sizing/responsive-iframe/resources/iframe-contents-unsized.html

@@ -9,5 +9,5 @@
     contain-intrinsic-size: from-element;
 }
 </style>
-<iframe frameborder=0 scrolling=no src="http://{{hosts[alt][]}}:{{ports[http][0]}}/css/css-sizing/resources/iframe-contents-unsized.html">
+<iframe frameborder=0 scrolling=no src="http://{{hosts[alt][]}}:{{ports[http][0]}}/css/css-sizing/responsive-iframe/resources/iframe-contents-unsized.html">
 </iframe>

css/css-sizing/resources/iframe-contents.html renamed to css/css-sizing/responsive-iframe/resources/iframe-contents.html

@@ -9,5 +9,5 @@
     contain-intrinsic-size: from-element;
 }
 </style>
-<iframe frameborder=0 src="http://{{hosts[alt][]}}:{{ports[http][0]}}/css/css-sizing/resources/iframe-contents.html">
+<iframe frameborder=0 src="http://{{hosts[alt][]}}:{{ports[http][0]}}/css/css-sizing/responsive-iframe/resources/iframe-contents.html">
 </iframe>