Roll DEPS for v8 to 47bcec7.

Regular, but overdue roll.

Review URL: https://codereview.chromium.org/1879923002
diff --git a/DEPS b/DEPS
index 02561ad..dc38a7d 100644
--- a/DEPS
+++ b/DEPS
@@ -12,7 +12,7 @@
   'pdfium_tests_revision': 'eb87214cb2088536e96aae517f3a281818fbf5b0',
   'skia_revision': '0a291c7b7eea1807bd58bdaa60c258fd0ebeb257',
   'trace_event_revision': 'd83d44b13d07c2fd0a40101a7deef9b93b841732',
-  'v8_revision': '3c3d7e7be80f45eeea0dc74a71d7552e2afc2985',
+  'v8_revision': '47bcec782b752ba411bd8bba6e390d1cc1c3226e',
 
 }