Revert of Disable flaky CommandLineExtensionsDontLoad test (patchset #1 id:1...

Revert of Disable flaky CommandLineExtensionsDontLoad test (patchset #1 id:1 of https://codereview.chromium.org/2852933002/ )

Reason for revert:
Speculatively reverting due to build failure on Mac https://build.chromium.org/p/chromium/builders/Mac/builds/26841

Original issue's description:
> Disable flaky CommandLineExtensionsDontLoad test
>
> TBR=emaxx@chromium.org
> BUG=716727
>
> Review-Url: https://codereview.chromium.org/2852933002
> Cr-Commit-Position: refs/heads/master@{#468286}
> Committed: https://chromium.googlesource.com/chromium/src/+/91f64acccbfe592af367f79ae74649d520528f0b

TBR=emaxx@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=716727

Review-Url: https://codereview.chromium.org/2855553002
Cr-Commit-Position: refs/heads/master@{#468290}

chrome/browser/extensions/extension_startup_browsertest.cc

@@ -284,9 +284,8 @@ class ExtensionsLoadTestWithLoginScreenApps : public ExtensionsLoadTest {
   }
 };
 
-// Flaky test crbug.com/716727
 IN_PROC_BROWSER_TEST_F(ExtensionsLoadTestWithLoginScreenApps,
-                       DISABLED_CommandLineExtensionsDontLoad) {
+                       CommandLineExtensionsDontLoad) {
   // The --load-extension command line flag should not be applied to the sign-in
   // profile.
   EXPECT_EQ(0, GetNonComponentEnabledExtensionCount(