Add asserts header.

// FREEBIE

src/Util/Asserts.h

@@ -0,0 +1,30 @@
+//
+//  Asserts.h
+//
+//  Copyright (c) 2016 Open Whisper Systems. All rights reserved.
+//
+
+#import <Foundation/Foundation.h>
+
+#ifndef OWSAssert
+
+#ifdef DEBUG
+
+#define USE_ASSERTS
+
+#define CONVERT_TO_STRING(X) #X
+#define CONVERT_EXPR_TO_STRING(X) CONVERT_TO_STRING(X)
+
+#define OWSAssert(X) \
+if (!(X)) { \
+NSLog(@"Assertion failed: %s", CONVERT_EXPR_TO_STRING(X)); \
+NSAssert(0, @"Assertion failed: %s", CONVERT_EXPR_TO_STRING(X)); \
+}
+
+#else
+
+#define OWSAssert(X)
+
+#endif
+
+#endif