Add gm/confirm_no_failures_in_json.py

gm/gm_expectations.cpp

Index: gm/gm_expectations.cpp
===================================================================
--- gm/gm_expectations.cpp	(revision 9118)
+++ gm/gm_expectations.cpp	(working copy)
@@ -11,6 +11,8 @@
 
 #define DEBUGFAIL_SEE_STDERR SkDEBUGFAIL("see stderr for message")
 
+// These constants must be kept in sync with the JSONKEY_ constants in
+// confirm_no_failures_in_json.py !
 const static char kJsonKey_ActualResults[]   = "actual-results";
 const static char kJsonKey_ActualResults_Failed[]        = "failed";
 const static char kJsonKey_ActualResults_FailureIgnored[]= "failure-ignored";