Skip failing pageset from key_mobile_sites_smooth

I would normally move the Chromium failing pagesets to be a Skia pageset but we used to have twitter.com/katyperry as a pageset a while ago and decided to remove it.

NoTry: true
Bug: skia:7348
Change-Id: I005b34b33f3bd2cc5e7948e1caad222156f36216
Reviewed-on: https://skia-review.googlesource.com/110120
Commit-Queue: Ravi Mistry <rmistry@google.com>
Reviewed-by: Ben Wagner <benjaminwagner@google.com>
diff --git a/tools/skp/webpages_playback.py b/tools/skp/webpages_playback.py
index dad9a39..4118160 100644
--- a/tools/skp/webpages_playback.py
+++ b/tools/skp/webpages_playback.py
@@ -106,7 +106,7 @@
 
 PAGE_SETS_TO_EXCLUSIONS = {
     # See skbug.com/7348
-    'key_mobile_sites_smooth.py': '"(digg|worldjournal)"',
+    'key_mobile_sites_smooth.py': '"(digg|worldjournal|Twitter)"',
     # See skbug.com/7421
     'top_25_smooth.py': '"(mail\.google\.com)"',
 }