Revert "WebUI: Cleanup unnecessary code duplication in cr_dialog."

This reverts commit f306830b.

Reason for revert: The if expression doesn't work mid tag on attributes on chromeos: http://screen/8GEEvG6Tpzzu8Ct.png

Original change's description:
> WebUI: Cleanup unnecessary code duplication in cr_dialog.
>
> At r819219 a large part of cr_dialog.html code was duplicated between
> CrOS/non-CrOS builds unnecessarily.
>
> Bug: 1007433
> Change-Id: Ia7de207202cdbd39f0b8d8671cd809249da36081
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2565184
> Commit-Queue: dpapad <dpapad@chromium.org>
> Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#831882}

TBR=khorimoto@chromium.org,dpapad@chromium.org

Change-Id: Ib7a20c91b4cfbf5e73b5d9b7b841788adb794ef5
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 1007433
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2567354Reviewed-by: James Vecore <vecore@google.com>
Commit-Queue: James Vecore <vecore@google.com>
Cr-Commit-Position: refs/heads/master@{#832237}

ui/webui/resources/cr_elements/cr_dialog/cr_dialog.html

@@ -148,14 +148,12 @@
         margin-top: 4px;
       }
     </style>
-    <!-- TODO(crbug/1139958): Remove "not chromeos" block when chromeVox issue
-        is fixed-->
+    <!-- TODO(crbug/1139958): Remove "not chromeos" block when chromeVox issue is fixed-->
+    <!--Update both "not chromeos" and "chromeos" blocks if either changes-->
+<if expr="not chromeos">
     <dialog id="dialog" on-close="onNativeDialogClose_"
         on-cancel="onNativeDialogCancel_" part="dialog"
-<if expr="not chromeos">
-        aria-labelledby="title"
-</if>
-        >
+        aria-labelledby="title">
     <!-- This wrapper is necessary, such that the "pulse" animation is not
         erroneously played when the user clicks on the outer-most scrollbar. -->
       <div id="content-wrapper" part="wrapper">
@@ -177,6 +175,32 @@
         <slot name="footer"></slot>
       </div>
     </dialog>
+</if>
+<if expr="chromeos">
+    <dialog id="dialog" on-close="onNativeDialogClose_"
+        on-cancel="onNativeDialogCancel_" part="dialog">
+    <!-- This wrapper is necessary, such that the "pulse" animation is not
+        erroneously played when the user clicks on the outer-most scrollbar. -->
+        <div id="content-wrapper" part="wrapper">
+          <div class="top-container">
+            <div id="title" class="title-container" tabindex="-1">
+              <slot name="title"></slot>
+            </div>
+            <cr-icon-button id="close" class="icon-clear"
+                hidden$="[[!showCloseButton]]" aria-label$="[[closeText]]"
+                on-click="cancel" on-keypress="onCloseKeypress_">
+            </cr-icon-button>
+          </div>
+          <slot name="header"></slot>
+          <div class="body-container" id="container" show-bottom-shadow
+              part="body-container">
+            <slot name="body"></slot>
+          </div>
+          <slot name="button-container"></slot>
+          <slot name="footer"></slot>
+        </div>
+    </dialog>
+</if>
   </template>
   <script src="cr_dialog.js"></script>
 </dom-module>