arc: Fix different font for buttons in OOBE

TEST=Manually
BUG=896221

Change-Id: I4be49faac0574372b52a009f912dabeb85ec7283
Reviewed-on: https://chromium-review.googlesource.com/c/1392110Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Yury Khmel <khmel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#619455}

chrome/browser/resources/chromeos/login/arc_terms_of_service.html

@@ -78,7 +78,8 @@
         <oobe-text-button id="arc-tos-accept-button"
             inverse on-tap="onAccept_"
             disabled="[[arcTosButtonsDisabled]]">
-          <div i18n-content="arcTermsOfServiceAcceptButton"></div>
+          <div id="arc-tos-accept-button-content"
+              i18n-content="arcTermsOfServiceAcceptButton"></div>
         </oobe-text-button>
       </div>
     </oobe-dialog>

chrome/browser/resources/chromeos/login/screen_arc_terms_of_service.js

@@ -616,7 +616,7 @@ login.createScreen('ArcTermsOfServiceScreen', 'arc-tos', function() {
         this.setMetricsMode(
             loadTimeData.getString('arcTextMetricsManagedEnabled'), true);
       }
-      this.getElement_('arc-tos-accept-button').textContent =
+      this.getElement_('arc-tos-accept-button-content').textContent =
           loadTimeData.getString(
               isDemoModeSetup ? 'arcTermsOfServiceAcceptAndContinueButton' :
                                 'arcTermsOfServiceAcceptButton');