crostini: Enable flag crostini-username by default

In addition, CrostiniInstallerUI::ClickInstallForTesting() is updated so
that it works no matter whether this flag is on or not, so if in an
unlikely event that we need to re-disable this flag, we do not need to
modify it again.

Bug: 1016195
Change-Id: I254057ffdff281c2ca01035953adfc737214b646
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2040635Reviewed-by: Julian Watson <juwa@google.com>
Commit-Queue: Jason Lin <lxj@google.com>
Cr-Commit-Position: refs/heads/master@{#739262}

chrome/browser/ui/webui/chromeos/crostini_installer/crostini_installer_ui.cc

@@ -156,12 +156,14 @@ bool CrostiniInstallerUI::can_close() {
 }
 
 void CrostiniInstallerUI::ClickInstallForTesting() {
-  // TODO(lxj): This assumes the config page does not show. When flag
-  // CrostiniUsername or CrostiniDiskResizing is turned on by default, we should
-  // click the "next" button first.
   web_ui()->GetWebContents()->GetMainFrame()->ExecuteJavaScriptForTests(
-      base::ASCIIToUTF16("document.querySelector('crostini-installer-app')"
-                         ".$.install.click()"),
+      base::ASCIIToUTF16(
+          "const app = document.querySelector('crostini-installer-app');"
+          // If flag CrostiniUsername or CrostiniDiskResizing is turned on,
+          // there will be a "next" button and we should click it to go to the
+          // config page before clicking "install" button.
+          "app.$$('#next:not([hidden])')?.click();"
+          "app.$.install.click();"),
       base::NullCallback());
 }
 

chromeos/constants/chromeos_features.cc

@@ -65,7 +65,7 @@ const base::Feature kCrostiniUseBusterImage{"CrostiniUseBusterImage",
 
 // Enables or disables Crostini Username picking.
 const base::Feature kCrostiniUsername{"CrostiniUsername",
-                                      base::FEATURE_DISABLED_BY_DEFAULT};
+                                      base::FEATURE_ENABLED_BY_DEFAULT};
 
 // Enables or disables Crostini GPU support.
 const base::Feature kCrostiniGpuSupport{"CrostiniGpuSupport",