Set width for destination dropdown

Use existing print preview sidebar variables to set the width the 192px.

Bug: 1059607
Change-Id: I173385684f57ddf204d5bb8c109d5e070381f3ae
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2284966
Commit-Queue: Gavin Williams <gavinwill@chromium.org>
Reviewed-by: Rebekah Potter <rbpotter@chromium.org>
Cr-Commit-Position: refs/heads/master@{#786624}

chrome/browser/resources/print_preview/ui/destination_dropdown_cros.html

 <style include="cr-shared-style cr-hidden-style">
+  #destination-dropdown {
+    position: relative;
+  }
+
+  #destination-dropdown,
+  iron-dropdown {
+    width: var(--print-preview-dropdown-width);
+  }
+
   iron-dropdown {
     border: 0.5px solid rgba(0, 0, 0, 0.5);
     max-height: 270px;
@@ -61,10 +70,6 @@
     padding-inline-start: 8px;
   }
 
-  #destination-dropdown {
-    position: relative;
-  }
-
   #destination-display-container {
     align-items: center;
     background-color: var(--google-grey-refresh-100);

chrome/browser/resources/print_preview/ui/destination_dropdown_cros.js

@@ -8,6 +8,8 @@ import 'chrome://resources/cr_elements/shared_vars_css.m.js';
 import 'chrome://resources/polymer/v3_0/iron-dropdown/iron-dropdown.js';
 import 'chrome://resources/polymer/v3_0/iron-icon/iron-icon.js';
 
+import './print_preview_vars_css.js';
+
 import {html, Polymer} from 'chrome://resources/polymer/v3_0/polymer/polymer_bundled.min.js';
 
 import {Destination, DestinationOrigin} from '../data/destination.js';

chrome/browser/resources/print_preview/ui/print_preview_vars_css.html

@@ -5,6 +5,10 @@
     --print-preview-sidebar-width: 384px;
     --print-preview-title-width: 120px;
     --print-preview-sidebar-margin: 24px;
+    /* Controls width = total width - title width - start/middle/end margin */
+    --print-preview-dropdown-width: calc(var(--print-preview-sidebar-width)
+        - var(--print-preview-title-width)
+        - 3 * var(--print-preview-sidebar-margin));
 
     --print-preview-settings-border: 1px solid var(--google-grey-200);
     --print-preview-dialog-margin: 34px;