Refine "[test] Skip webkit test too slow for ppc."

Skip only for simulator runs.

R=machenbach@chromium.org
BUG=

Review URL: https://codereview.chromium.org/1418593005

Cr-Commit-Position: refs/heads/master@{#31418}

test/webkit/webkit.status

@@ -66,7 +66,7 @@
   # Too slow for mips big-endian boards on bots (no FPU).
   'dfg-int-overflow-in-loop': [SKIP],
 }], # 'arch == mips'
-['arch == ppc or arch == ppc64', {
+['(arch == ppc or arch == ppc64) and simulator_run == True', {
   # Too slow.
   'dfg-int-overflow-in-loop': [SKIP],
 }], # 'arch == ppc or arch == ppc64'