Gate CrashHandler with SK_CRASH_HANDLER.

tools/CrashHandler.h

Index: tools/CrashHandler.h
diff --git a/tools/CrashHandler.h b/tools/CrashHandler.h
index 6c22c8ee705836cebba5cca94aacf7b5496d8fa0..606e81ef75d78fc5e8ee1968a43af684782db45f 100644
--- a/tools/CrashHandler.h
+++ b/tools/CrashHandler.h
@@ -1,9 +1,11 @@
 #ifndef CrashHandler_DEFINED
 #define CrashHandler_DEFINED
 
-// If possible (and not already done) register a handler for a stack trace when we crash.
-// Currently this works on Linux and Mac, hopefully Windows soon.
-// On Linux, you will get much better results than we can deliver by running "catchsegv <program>".
+// If possible (and not already done), and SK_CRASH_HANDLER is defined,
+// register a handler for a stack trace when we crash.
+//
+// Currently this works on Linux and Mac and Windows, but on Linux, you will
+// get much better results than we can deliver by running "catchsegv <program>".
 void SetupCrashHandler();
 
 #endif//CrashHandler_DEFINED