Files.app: Hide loading indicator on launch.

BUG=475377
TEST=manually

Review URL: https://codereview.chromium.org/1071033003

Cr-Commit-Position: refs/heads/master@{#324397}

ui/file_manager/file_manager/main.html

@@ -469,7 +469,7 @@
                 <div class="detail-table" id="detail-table" tabindex="1" autofocus>
                 </div>
                 <grid class="thumbnail-grid" tabindex="2"></grid>
-                <paper-progress class="loading-indicator" indeterminate></paper-progress>
+                <paper-progress class="loading-indicator" indeterminate hidden></paper-progress>
                 <div class="drive-welcome page"></div>
                 <div id="no-search-results"></div>
               </div>