Revert of Disable flaky ExperimentalAppWindowApiTest.SetIcon (patchset #1 id:1...

Revert of Disable flaky ExperimentalAppWindowApiTest.SetIcon (patchset #1 id:1 of https://codereview.chromium.org/2849073003/ )

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 ExperimentalAppWindowApiTest.SetIcon
>
> TBR=benwells@chromium.org
> BUG=716726
>
> Review-Url: https://codereview.chromium.org/2849073003
> Cr-Commit-Position: refs/heads/master@{#468285}
> Committed: https://chromium.googlesource.com/chromium/src/+/78552aab8b749f33cd8176a977bdff4fa7d5de50

TBR=benwells@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=716726

Review-Url: https://codereview.chromium.org/2855563002
Cr-Commit-Position: refs/heads/master@{#468289}

extensions/browser/api/app_window/app_window_apitest.cc

@@ -62,8 +62,7 @@ using AppWindowApiTest = PlatformAppBrowserTest;
 using ExperimentalAppWindowApiTest = ExperimentalPlatformAppBrowserTest;
 
 // Tests chrome.app.window.setIcon.
-// Flaky test crbug.com/716726
-IN_PROC_BROWSER_TEST_F(ExperimentalAppWindowApiTest, DISABLED_SetIcon) {
+IN_PROC_BROWSER_TEST_F(ExperimentalAppWindowApiTest, SetIcon) {
   std::unique_ptr<TestAppWindowRegistryObserver> test_observer(
       new TestAppWindowRegistryObserver(browser()->profile()));
   ExtensionTestMessageListener listener("ready", true);