Fix dependency for Assistant opt-in dialog

Include oobe.css for the newly added CSS variables.

Bug: 1012793
Test: Manual Test
Change-Id: If67e43f454b9ccf193029c8b144ef45062d057ba
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1864364Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Yue Li <updowndota@chromium.org>
Cr-Commit-Position: refs/heads/master@{#707032}

chrome/browser/resources/chromeos/assistant_optin/assistant_optin.html

@@ -26,6 +26,8 @@
 <link rel="stylesheet" href="chrome://resources/css/chrome_shared.css">
 <link rel="stylesheet" href="../login/oobe_flex_layout.css">
 <link rel="stylesheet" href="../login/oobe_screen.css">
+<link rel="stylesheet" href="../login/oobe_dialog.css">
+<link rel="stylesheet" href="../../../../../ui/login/oobe.css">
 <link rel="stylesheet" href="setting_zippy.css">
 <style include="cr-icons cr-shared-style"></style>
 

chrome/browser/resources/chromeos/login/oobe_dialog.css

@@ -13,9 +13,9 @@
 
 #header-container {
   padding-bottom: 0;
-  padding-inline-end: var(--oobe-dialog-content-padding, 64px);
-  padding-inline-start: var(--oobe-dialog-content-padding, 64px);
-  padding-top: var(--oobe-dialog-content-padding, 64px);
+  padding-inline-end: var(--oobe-dialog-content-padding);
+  padding-inline-start: var(--oobe-dialog-content-padding);
+  padding-top: var(--oobe-dialog-content-padding);
 }
 
 #header-container[android] {
@@ -56,7 +56,7 @@
 
 #footer-container {
   overflow-y: auto;
-  padding: 0 var(--oobe-dialog-content-padding, 64px);
+  padding: 0 var(--oobe-dialog-content-padding);
 }
 
 #footer-container[noFooterPadding] {
@@ -64,11 +64,11 @@
 }
 
 #oobe-bottom {
-  height: calc(var(--oobe-dialog-footer-height, 96px)
-               - 2 * var(--oobe-dialog-footer-padding, 32px));
+  height: calc(var(--oobe-dialog-footer-height)
+               - 2 * var(--oobe-dialog-footer-padding));
   /* Width: real padding - button margin */
-  padding: var(--oobe-dialog-footer-padding, 32px)
-           calc(var(--oobe-dialog-footer-padding, 32px) - 4px);
+  padding: var(--oobe-dialog-footer-padding)
+           calc(var(--oobe-dialog-footer-padding) - 4px);
   z-index: 1;
 }