Implemented AddAllocWithZoneMethod to override allocWithZone: on demand.

ios/web/alloc_with_zone_interceptor_unittest.mm

Index: ios/web/alloc_with_zone_interceptor_unittest.mm
diff --git a/ios/web/alloc_with_zone_interceptor_unittest.mm b/ios/web/alloc_with_zone_interceptor_unittest.mm
new file mode 100644
index 0000000000000000000000000000000000000000..7b4a1953067fbada6d29c2dd3bb737828e24a5b6
--- /dev/null
+++ b/ios/web/alloc_with_zone_interceptor_unittest.mm
@@ -0,0 +1,36 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#import "ios/web/alloc_with_zone_interceptor.h"
+
+#include "testing/gtest/include/gtest/gtest.h"
+#include "testing/gtest_mac.h"
+#include "testing/platform_test.h"
+
+// Testable class to test web::AddAllocWithZoneMethod.
+@interface CRBTestAlloc : NSObject
+@end
+@implementation CRBTestAlloc
+@end
+
+namespace web {
+namespace {
+
+// Test class for alloc_with_zone_interceptor functions.

[shreyasv1, 2015/04/08 22:36:20]

Wording NIT: This is actually a Test Fixture.

[Eugene But (OOO till 7-30), 2015/04/08 23:02:12]

Done.

+typedef PlatformTest AllocWithZoneInterceptorTest;
+
+// Tests that AddAllocWithZoneMethod delegates allocation to the caller.
+TEST_F(AllocWithZoneInterceptorTest, AddAllocWithZoneMethod) {
+  NSString* const kResult = @"test-result";
+  NSZone* const kZone = NSDefaultMallocZone();

[shreyasv1, 2015/04/08 22:36:20]

Optional: Given that NSDefaultMallocZone returns the same NSZone for every call
(Idempotent?). Maybe just inline this?

[Eugene But (OOO till 7-30), 2015/04/08 23:02:12]

I have kResult, having kZone seems consistent.

+  AddAllocWithZoneMethod([CRBTestAlloc class], ^id(Class klass, NSZone* zone) {
+    EXPECT_EQ([CRBTestAlloc class], klass);
+    EXPECT_EQ(kZone, zone);
+    return kResult;
+  });
+  EXPECT_NSEQ(kResult, [CRBTestAlloc allocWithZone:kZone]);
+}
+
+}  // namespace
+}  // namespace web