[Cronet] Add BUILD.gn for legacy ios/CrNet project.

ios/crnet/crnet_consumer/crnet_consumer_app_delegate.mm

 // Copyright 2014 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 "crnet_consumer_app_delegate.h"
 
-#import "CrNet.h"
+#import "ios/crnet/CrNet.h"

[sdefresne, 2016/08/02 21:54:11]

If you follow my recommendation about using crnet_framework+{bind,bundle}, I
think you will have to revert those #import changes.

[mef, 2016/08/03 20:42:41]

Using crnet_framework+bind results in gn error and using crnet_framework+link
still needs path to the header file. Any ideas?

 #include "base/format_macros.h"
 #import "crnet_consumer_view_controller.h"
 
 @implementation CrNetConsumerAppDelegate {
   NSUInteger _counter;
 }
 
 @synthesize window;
 @synthesize viewController;
 
@@ skipping 62 matching lines @@
     NSLog(@"Cache cleared: %d\n", error);
   }];
 }
 
 - (void)applicationWillEnterForeground:(UIApplication*)application {
   _counter++;
   [CrNet startNetLogToFile:[self currentNetLogFileName] logBytes:NO];
 }
 
 @end