CUPS: Fix the regression that BROWSE button is missing in Add Printer dialog.

Bug: 814631
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: I8456707c5d72052e1dbda6a364d6b2c1d2a7ec8b
Reviewed-on: https://chromium-review.googlesource.com/952084
Commit-Queue: Xiaoqian Dai <xdai@chromium.org>
Reviewed-by: Hector Carmona <hcarmona@chromium.org>
Cr-Commit-Position: refs/heads/master@{#541539}

chrome/browser/resources/settings/printing_page/cups_add_printer_dialog.html

@@ -224,7 +224,7 @@
                   value="[[getBaseName_(activePrinter.printerPPDPath)]]"
                   error-message="$i18n{selectDriverErrorMessage}"
                   invalid="[[invalidPPD]]">
-                <paper-button class="browse-button" suffix
+                <paper-button class="browse-button" slot="suffix"
                     on-click="onBrowseFile_">
                   $i18n{selectDriverButtonText}
                 </paper-button>

chrome/browser/resources/settings/printing_page/cups_edit_printer_dialog.html

@@ -100,7 +100,7 @@
             <div class="secondary">
               <paper-input class="browse-file-input" no-label-float readonly
                   value="[[getBaseName_(activePrinter.printerPPDPath)]]">
-                <paper-button class="browse-button" suffix
+                <paper-button class="browse-button" slot="suffix"
                     on-click="onBrowseFile_">
                   $i18n{selectDriverButtonText}
                 </paper-button>