Closure compile mock_progess_center

Add a work-around for CSSRule.KEYFRAMES_RULE not being defined Closure,
which does not define experimental web features.

No change in behavior, no new tests.

Bug: 907962
No-presubmit: true
Change-Id: I4dd62588da812dbea641be898cf908056a842257
Reviewed-on: https://chromium-review.googlesource.com/c/1349147
Commit-Queue: Noel Gordon <noel@chromium.org>
Reviewed-by: Stuart Langley <slangley@chromium.org>
Cr-Commit-Position: refs/heads/master@{#610541}

ui/file_manager/file_manager/background/js/BUILD.gn

@@ -67,6 +67,7 @@ js_type_check("test_support_type_check") {
   testonly = true
   deps = [
     ":mock_media_scanner",
+    ":mock_progress_center",
     ":mock_volume_manager",
     ":test_import_history",
   ]
@@ -309,13 +310,22 @@ js_library("mock_volume_manager") {
   ]
 }
 
+js_library("mock_progress_center") {
+  testonly = true
+
+  deps = [
+    ":progress_center",
+  ]
+
+  externs_list = [ "//ui/file_manager/externs/background/progress_center.js" ]
+}
+
 js_library("progress_center") {
   deps = [
     "../../common/js:async_util",
     "../../common/js:progress_center_common",
     "../../common/js:util",
     "../../foreground/js/ui:progress_center_panel",
-
   ]
 
   externs_list = [ "//ui/file_manager/externs/background/progress_center.js" ]

ui/file_manager/file_manager/foreground/js/ui/progress_center_panel.js

@@ -276,8 +276,10 @@ ProgressCenterPanel.getToggleAnimation_ = function(document) {
   for (var i = 0; i < document.styleSheets.length; i++) {
     var styleSheet = document.styleSheets[i];
     for (var j = 0; j < styleSheet.cssRules.length; j++) {
+      // HACK: closure does not define experimental CSSRules.
+      var keyFramesRule = CSSRule.KEYFRAMES_RULE || 7;
       var rule = styleSheet.cssRules[j];
-      if (rule.type === CSSRule.KEYFRAMES_RULE &&
+      if (rule.type === keyFramesRule &&
           rule.name === 'progress-center-toggle') {
         return rule;
       }