Files.app: Add UI to toggle and clear item selection.

ui/file_manager/file_manager/main.html

Index: ui/file_manager/file_manager/main.html
diff --git a/ui/file_manager/file_manager/main.html b/ui/file_manager/file_manager/main.html
index ecc0afb068f4890b3e77b7b1f521a50de02c5f33..8a28503cf578925ab2a908b318532cbc75313500 100644
--- a/ui/file_manager/file_manager/main.html
+++ b/ui/file_manager/file_manager/main.html
@@ -131,6 +131,7 @@
       <script src="foreground/js/share_client.js"></script>
       <script src="foreground/js/spinner_controller.js"></script>
       <script src="foreground/js/task_controller.js"></script>
+      <script src="foreground/js/toolbar_controller.js"></script>
       <script src="foreground/js/thumbnail_loader.js"></script>
       <script src="foreground/js/ui/banners.js"></script>
       <script src="foreground/js/ui/conflict_dialog.js"></script>
@@ -301,6 +302,10 @@
 
     <div class="dialog-header">
       <div id="location-breadcrumbs" class="breadcrumbs"></div>
+      <paper-button id="cancel-selection-button">
+        <core-icon icon="arrow-back" style="width:16px; height:16px"></core-icon>
+        <span i18n-content="CANCEL_SELECTION_BUTTON_LABEL"></span>
+      </paper-button>
       <div id="files-selected-label"></div>
       <div class="spacer"></div>
       <button id="tasks" class="combobutton" menu="#tasks-menu"