Files app: Fix FileManagerJsTest to work without DOMv0 and HTML Imports

Change the generated HTML to include the HTML import polyfil and to not
include the scripts from <cr_elements> because they'll be included via
HTML imports by the elements that use them.

Change the test harness to detect if HTML Import polyfil is available
and wait for imports to finish before starting the test.

Bug: 1111393
Change-Id: I2a8d55bee39f8386e75183bcbb79fbbf15204d03
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2362167
Commit-Queue: Luciano Pacheco <lucmult@chromium.org>
Reviewed-by: dpapad <dpapad@chromium.org>
Reviewed-by: Mason Freed <masonfreed@chromium.org>
Cr-Commit-Position: refs/heads/master@{#799934}

chrome/renderer/chrome_content_renderer_client.cc

@@ -1669,9 +1669,6 @@ bool ChromeContentRendererClient::RequiresWebComponentsV0(const GURL& url) {
            host_piece == chrome::kChromeUIOSSettingsHost ||
            // TODO(crbug.com/1022192): Remove when migrated to Polymer3.
            host_piece == chrome::kChromeUIPasswordChangeHost ||
-           // TODO(crbug.com/1111393): Remove when migrated away from HTML
-           // imports.
-           host_piece == "file_manager_test" ||
 #endif
            false;
   }

ui/file_manager/base/gn/js_test_gen_html.py

@@ -24,6 +24,8 @@ window.addEventListener('error', function(e) {
 
 _SCRIPT = r'<script src="%s"></script>'
 _IMPORT = r'<link rel="import" href="%s">'
+_HTML_IMPORT_POLYFIL =  _SCRIPT  % (
+    'chrome://resources/polymer/v1_0/html-imports/html-imports.min.js')
 
 _HTML_FOOTER = r"""
 </body>
@@ -45,6 +47,10 @@ def _process_deps(unique_deps, html_import, target_name):
     Iterator of strings, each string is a HTML tag <script> or <link>.
   """
   for dep in unique_deps:
+    # Scripts from cr_elements are included via HTML imports.
+    if '/cr_elements/' in dep:
+      continue
+
     # Special case for jstemplate which has multiple files but we server all of
     # them combined from chrome://resources/js/jstemplate_compiled.js
     if '/jstemplate/' in dep:
@@ -104,6 +110,10 @@ def _process(deps, output_filename, mocks, html_import, target_name):
 
   with open(output_filename, 'w') as out:
     out.write(_HTML_FILE)
+
+    if html_import:
+      out.write(_HTML_IMPORT_POLYFIL + '\n')
+
     for dep in _process_deps(mocks, html_import, target_name):
       out.write(dep + '\n')
     for dep in _process_deps(deps, html_import, target_name):

ui/webui/resources/js/webui_resource_test.js

@@ -227,7 +227,14 @@ function startTesting() {
     setTimeout(startTesting, 1000);
     return;
   }
-  continueTesting();
+
+  if (window.HTMLImports && window.HTMLImports.whenReady) {
+    /// When there is a HTML Import polyfill wait all imports to finish before
+    // starting the test.
+    window.HTMLImports.whenReady(continueTesting);
+  } else {
+    continueTesting();
+  }
 }
 
 /**