[test] Skip webkit test too slow for ppc.

NOTRY=true
TBR=mbrandy@us.ibm.com

Review URL: https://codereview.chromium.org/1411993004

Cr-Commit-Position: refs/heads/master@{#31396}

test/webkit/webkit.status

@@ -66,6 +66,10 @@
   # Too slow for mips big-endian boards on bots (no FPU).
   'dfg-int-overflow-in-loop': [SKIP],
 }], # 'arch == mips'
+['arch == ppc or arch == ppc64', {
+  # Too slow.
+  'dfg-int-overflow-in-loop': [SKIP],
+}], # 'arch == ppc or arch == ppc64'
 
 ##############################################################################
 ['asan == True', {