Mash: enable PDFExtensionHitTestTest.MouseLeave/1

Works after 127968d6

Bug: 879308
Change-Id: Ic49eb7e0a1af70cf0701930631c6956069d4e709
Reviewed-on: https://chromium-review.googlesource.com/c/1321572Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Evan Stade <estade@chromium.org>
Cr-Commit-Position: refs/heads/master@{#605917}

testing/buildbot/filters/chromeos.single_process_mash.browser_tests.filter

@@ -29,9 +29,6 @@
 -SelectToSpeak*
 -SwitchAccess*
 
-# Viz hit testing not supported with Mash https://crbug.com/879308
--PDFExtensionHitTestTest.MouseLeave/1
-
 # Flaky. https://crbug.com/888188.
 -ChromeSessionManagerTest.LoginExistingUsers
 -ChromeSessionManagerTest.PRE_LoginExistingUsers