Revert of Disable BrowserTest.InterstitialCloseTab which is flaky. (patchset...

Revert of Disable BrowserTest.InterstitialCloseTab which is flaky. (patchset #1 id:1 of https://codereview.chromium.org/424143003/)

Reason for revert:
This should be fixed by r288895

Original issue's description:
> Disable BrowserTest.InterstitialCloseTab which is flaky.
>
> BUG=393218
> TBR=mattm@chromium.org
> NOTRY=true
>
> Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=286225

TBR=mattm@chromium.org,jam@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=393218

Review URL: https://codereview.chromium.org/523733003

Cr-Commit-Position: refs/heads/master@{#292707}

chrome/browser/ui/browser_browsertest.cc

@@ -1981,13 +1981,8 @@ IN_PROC_BROWSER_TEST_F(BrowserTest, InterstitialClosesDialogs) {
   EXPECT_FALSE(contents->GetRenderProcessHost()->IgnoreInputEvents());
 }
 
-#if defined(OS_MACOSX)
-// http://crbug.com/393218
-#define MAYBE_InterstitialCloseTab DISABLED_InterstitialCloseTab
-#else
-#define MAYBE_InterstitialCloseTab InterstitialCloseTab
-#endif
-IN_PROC_BROWSER_TEST_F(BrowserTest, MAYBE_InterstitialCloseTab) {
+
+IN_PROC_BROWSER_TEST_F(BrowserTest, InterstitialCloseTab) {
   WebContents* contents = browser()->tab_strip_model()->GetActiveWebContents();
 
   {