Disable FindInPageControllerTest.FindLongString on Mac debug builds

Looks like FindLongString is supposed to be disabled on Mac debug testers but the test name wasn't changed over to the MAYBE_ prefix.

Recent flake: https://logs.chromium.org/logs/chromium/buildbucket/cr-buildbucket.appspot.com/8869619630837658832/+/steps/browser_tests_on__none__GPU_on_Mac_on_Mac-10.13.6/0/logs/Deterministic_failure:_FindInPageControllerTest.FindLongString__status_FAILURE_TIMEOUT_/0

Bug: 1096911
Tbr: justincohen@chromium.org,skhapugin@chromium.org
Change-Id: I213df7a630ffb9cdf025b3e80a32c389ba14db78
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2401868Reviewed-by: David Van Cleve <davidvc@chromium.org>
Commit-Queue: David Van Cleve <davidvc@chromium.org>
Cr-Commit-Position: refs/heads/master@{#805455}

chrome/browser/ui/find_bar/find_bar_host_browsertest.cc

@@ -442,7 +442,7 @@ IN_PROC_BROWSER_TEST_F(FindInPageControllerTest, MAYBE_LargePage) {
 #else
 #define MAYBE_FindLongString FindLongString
 #endif
-IN_PROC_BROWSER_TEST_F(FindInPageControllerTest, FindLongString) {
+IN_PROC_BROWSER_TEST_F(FindInPageControllerTest, MAYBE_FindLongString) {
   WebContents* web_contents =
       browser()->tab_strip_model()->GetActiveWebContents();
   ui_test_utils::NavigateToURL(browser(), GetURL("largepage.html"));