FileManagerUITest.CrostiniShare timeout fix

Some test logs show an error clicking on 'photos' folder after going
back to the root of MyFiles, so adding a waitForFiles call immediately
after clikcing MyFiles to wait for all files (including photos) to be
visible.

https://logs.chromium.org/logs/chromium/buildbucket/cr-buildbucket.appspot.com/8867151645799555504/+/steps/browser_tests__with_patch_/0/logs/Flaky_failure:_FileManagerUITest.CrostiniShare__status_SUCCESS_TIMEOUT_/0

And while I'm here, fix the comment in filemanager_uitest.cc. The
--disable-web-security flag allows files to be loaded, but has no affect
on chrome:// urls - I don't why I ever wrote that (⌒_⌒;)

Bug: 1135410
Change-Id: I9f5a97bb0a209a9590a2a55721cc420cec19ceb3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2454551
Commit-Queue: Fergus Dall <sidereal@google.com>
Auto-Submit: Joel Hockey <joelhockey@chromium.org>
Reviewed-by: Fergus Dall <sidereal@google.com>
Cr-Commit-Position: refs/heads/master@{#814548}

chrome/browser/chromeos/file_manager/file_manager_uitest.cc

@@ -20,8 +20,7 @@ namespace file_manager {
 class FileManagerUITest : public InProcessBrowserTest {
  public:
   void SetUpCommandLine(base::CommandLine* command_line) override {
-    // --disable-web-security required to load resources from
-    // files and from chrome://resources/... urls.
+    // --disable-web-security required to load resources from files.
     command_line->AppendSwitch(switches::kDisableWebSecurity);
   }
 

ui/file_manager/file_manager/test/crostini_share.js

@@ -144,6 +144,8 @@ shareBase.testSharePaths = async (
 
   // Go back to 'My files' and ensure message is not shown.
   assertTrue(test.fakeMouseDoubleClick(myFilesDirTree), 'click My files');
+  await test.waitForFiles(test.TestEntryInfo.getExpectedRows(
+      test.BASIC_MY_FILES_ENTRY_SET_WITH_LINUX_FILES));
   await test.waitForElement(shareMessageHidden);
 
   // Dispatch unshare event which is normally initiated when the user