Re-enable PluginPowerSaverBrowserTest on Viz

It appears that PluginPowerSaverBrowserTest.SmallerThanPlayIcon on Mac for Viz
has begun working again. This re-enables it.

TBR=kylechar@chromium.org
TEST=PluginPowerSaverBrowserTest.SmallerThanPlayIcon

Bug: 823276
Change-Id: I6333f40c20da0622cc8bfe45da486922471e8307
Reviewed-on: https://chromium-review.googlesource.com/1069656Reviewed-by: Jonathan Ross <jonross@chromium.org>
Cr-Commit-Position: refs/heads/master@{#561043}

testing/buildbot/filters/viz.browser_tests.filter

@@ -17,11 +17,7 @@
 -WebViewTest.ReloadAfterCrash
 -WebViewGuestTouchFocusBrowserPluginSpecificTest.TouchFocusesBrowserPluginInEmbedder
 
-# Mac
-# Shutdown error. https://crbug.com/823276
--PluginPowerSaverBrowserTest.SmallerThanPlayIcon
-
-# Flaking with missing browser. https://crbug.com/842664
+# Mac Flaking with missing browser. https://crbug.com/842664
 -IndependentOTRProfileManagerTest.DeleteImmediatelyWhenBrowsersAlreadyClosed
 
 # https://crbug.com/843921