Added unpacking step

chrome/installer/mac/app/Unpacker.h

+// Copyright 2016 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.
+
+#ifndef CHROME_INSTALLER_MAC_APP_UNPACKER_H_
+#define CHROME_INSTALLER_MAC_APP_UNPACKER_H_
+
+#import <Foundation/Foundation.h>
+
+// TODO: revise api to be more succinct & logical, make the unnecessary ones
+// potentially optional for testing's sake
+
+@class Unpacker;
+@protocol UnpackDelegate
+- (void)unpacker:(Unpacker*)unpacker onMountSuccess:(NSString*)mountpath;
+- (void)unpacker:(Unpacker*)unpacker onMountFailure:(NSString*)mountpath;
+- (void)unpacker:(Unpacker*)unpacker onExtractSuccess:(NSString*)appPath;
+- (void)unpacker:(Unpacker*)unpacker onExtractFailure:(NSString*)appPath;
+// TODO: put in a better parameter to pass through
+- (void)unpacker:(Unpacker*)unpacker onUnmountSuccess:(NSError*)error;
+- (void)unpacker:(Unpacker*)unpacker onUnmountFailure:(NSError*)error;
+@end
+
+@interface Unpacker : NSObject
+
+@property(nonatomic, assign) id<UnpackDelegate> delegate;
+@property(nonatomic, copy) NSString* appPath;
+
+- (id)initWithFinalAppPath:(NSString*)appPath;
+
+// TODO: write a new "extracter" class to be nested into unpacker
+- (void)mountDMGFromURL:(NSURL*)fileURL;
+- (void)extractChrome;
+- (void)unmountDMG;
+
+@end
+
+#endif  // CHROME_INSTALLER_MAC_APP_UNPACKER_H_