Enable ChromeLauncherControllerWithArcTest.ArcAppPinPolicy test

This reverts commit 7476d68c.

Reason for revert: The cause of test flakiness was fixed in
https://crrev.com/c/1092851.

Original change's description:
> Disable flaking ChromeLauncherControllerWithArcTest.ArcAppPinPolicy
> 
> ChromeLauncherControllerWithArcTest.ArcAppPinPolicy is flaking currently.
> Disabling as the team who owns the root cause is OOO.
> 
> TEST=ChromeLauncherControllerWithArcTest.ArcAppPinPolicy
> TBR=skuhne@chromium.org
> 
> Bug: 839916
> Change-Id: I86209df361ab53cb84225363c39b1c83db197a2f
> Reviewed-on: https://chromium-review.googlesource.com/1044655
> Reviewed-by: Jonathan Ross <jonross@chromium.org>
> Commit-Queue: Jonathan Ross <jonross@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#556125}

TBR=skuhne@chromium.org,jonross@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 839916
Change-Id: I36936a7a97b04857a20d892a636f6aac98bc04b2
Reviewed-on: https://chromium-review.googlesource.com/1122796Reviewed-by: Alexandr Ilin <alexilin@chromium.org>
Commit-Queue: Alexandr Ilin <alexilin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#571902}

chrome/browser/ui/ash/launcher/chrome_launcher_controller_unittest.cc

@@ -3761,8 +3761,7 @@ TEST_F(ChromeLauncherControllerTest, MultipleAppIconLoaders) {
   EXPECT_EQ(1, app_icon_loader2->clear_count());
 }
 
-// Test is flaking. https://crbug.com/839916
-TEST_P(ChromeLauncherControllerWithArcTest, DISABLED_ArcAppPinPolicy) {
+TEST_P(ChromeLauncherControllerWithArcTest, ArcAppPinPolicy) {
   InitLauncherControllerWithBrowser();
   arc::mojom::AppInfo appinfo =
       CreateAppInfo("Some App", "SomeActivity", "com.example.app");