Revert recent changes to the Fullscreen UA style sheet

Source/core/css/fullscreen.css

-/*
- * User-agent level style sheet defaults for the Fullscreen API
- * https://fullscreen.spec.whatwg.org/#user-agent-level-style-sheet-defaults
- *
- * FIXME: Use the :fullscreen pseudo-class instead of :-webkit-full-screen.
- * (see crbug.com/402378)
- */
-
-:not(:root):-webkit-full-screen {
-    position: fixed !important;
-    top: 0 !important;
-    right: 0 !important;
-    bottom: 0 !important;
-    left: 0 !important;
-    margin: 0 !important;
-    box-sizing: border-box !important;
-    min-width: 0 !important;
-    max-width: none !important;
-    min-height: 0 !important;
-    max-height: none !important;
-    width: 100% !important;
-    height: 100% !important;
-    object-fit: contain !important;
-    transform: none !important;
-}
-
-iframe:-webkit-full-screen {
-    border: none !important;
-    padding: 0 !important;
-}
-
-/* Anything below are extensions over what the Fullscreen API mandates. */
-
-/* FIXME: Remove these rules when moving Fullscreen to top layer.
-   (see crbug.com/240576) */
 :-webkit-full-screen {
     background-color: white;
     z-index: 2147483647 !important;
 }
 
-video:-webkit-full-screen, audio:-webkit-full-screen {
-    background-color: transparent !important;
+:root:-webkit-full-screen-ancestor {
+    overflow: hidden !important;
 }
 
 :-webkit-full-screen-ancestor:not(iframe) {
     z-index: auto !important;
     position: static !important;
     opacity: 1 !important;
     transform: none !important;
     -webkit-mask: none !important;
     clip: none !important;
     -webkit-filter: none !important;
     transition: none !important;
     -webkit-box-reflect: none !important;
     -webkit-perspective: none !important;
     -webkit-transform-style: flat !important;
 }
 
-/* This prevents video from overflowing the viewport in
-   virtual/android/fullscreen/video-scrolled-iframe.html
-   FIXME: We should remove this (see crbug.com/441890). */
-:-webkit-full-screen-ancestor {
-    overflow: hidden !important;
+video:-webkit-full-screen, audio:-webkit-full-screen {
+    background-color: transparent !important;
+    position: relative !important;
+    left: 0 !important;
+    top: 0 ! important;
+    margin: 0 !important;
+    min-width: 0 !important;
+    max-width: none !important;
+    min-height: 0 !important;
+    max-height: none !important;
+    width: 100% !important;
+    height: 100% !important;
+    flex: 1 !important;
+    display: block !important;
+    transform: none !important;
 }
+
+img:-webkit-full-screen {
+    width: auto;
+    height: 100%;
+    max-width: 100%;
+}
+
+iframe:-webkit-full-screen {
+    margin: 0 !important;
+    padding: 0 !important;
+    border: 0 !important;
+    position: fixed !important;
+    min-width: 0 !important;
+    max-width: none !important;
+    min-height: 0 !important;
+    max-height: none !important;
+    width: 100% !important;
+    height: 100% !important;
+    left: 0 !important;
+    top: 0 !important;
+}