WebUI MD Refresh: Update PDF password dialog buttons.

Bug: 853958
Cq-Include-Trybots: luci.chromium.try:closure_compilation
Change-Id: I1a9848f3bb1cba427e229b387516ffa1764c1096
Reviewed-on: https://chromium-review.googlesource.com/1105401Reviewed-by: Scott Chen <scottchen@chromium.org>
Commit-Queue: Demetrios Papadopoulos <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#568280}

chrome/browser/resources/pdf/elements/viewer-password-screen/viewer-password-screen.html

@@ -3,11 +3,12 @@
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-input/paper-input.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-styles/color.html">
 <link rel="import" href="chrome://resources/cr_elements/cr_dialog/cr_dialog.html">
+<link rel="import" href="chrome://resources/cr_elements/paper_button_style_css.html">
 <link rel="import" href="chrome://resources/cr_elements/shared_style_css.html">
 
 <dom-module id="viewer-password-screen">
   <template>
-    <style include="cr-shared-style">
+    <style include="cr-shared-style paper-button-style">
       #password {
         --paper-input-container-focus-color: var(--google-blue-500);
         --paper-input-container-input: {