[pulse] Add model for NSObject.init

Summary:
This model is very important in the analysis of ObjC classes because the pattern

```
- (instancetype)init {
  if (self = [super init]) {
    ...
  }
  return self;
}

```

is very common, so we need to know that if the super class is `NSObject`, the implementation of `init` is returning `self`, otherwise it's a skip function and we don't get the correct spec for the function.  We fix some memory leak FP with this model, see test.

Reviewed By: ezgicicek

Differential Revision: D22259281

fbshipit-source-id: 3ee48c827

infer/src/pulse/PulseModels.ml

@@ -985,7 +985,8 @@ module ProcNameDispatcher = struct
         ; -"CFBridgingRelease" <>$ capt_arg_payload $--> ObjCCoreFoundation.cf_bridging_release
         ; +match_builtin BuiltinDecl.__objc_bridge_transfer
           <>$ capt_arg_payload $--> ObjCCoreFoundation.cf_bridging_release
-        ; +match_builtin BuiltinDecl.__objc_alloc_no_fail <>$ capt_exp $--> ObjC.alloc_not_null ] )
+        ; +match_builtin BuiltinDecl.__objc_alloc_no_fail <>$ capt_exp $--> ObjC.alloc_not_null
+        ; -"NSObject" &:: "init" <>$ capt_arg_payload $--> Misc.id_first_arg ] )
 end
 
 let dispatch tenv proc_name args = ProcNameDispatcher.dispatch tenv proc_name args

infer/tests/codetoanalyze/objc/pulse/NSObjectInitModelTest.m

@@ -0,0 +1,32 @@
+/*
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+#include <Foundation/NSObject.h>
+#include <stdlib.h>
+
+@interface MyBufferContainer : NSObject
+
+@property char* buffer;
+
+@end
+
+@implementation MyBufferContainer
+
+- (instancetype)init {
+  if (self = [super init]) {
+    _buffer = malloc(sizeof(char));
+  }
+  return self;
+}
+
+- (void)dealloc {
+  free(_buffer);
+}
+
+@end
+void raii_no_leak_ok() {
+  MyBufferContainer* b = [[MyBufferContainer alloc] init];
+}