Create headerHeightForTab in TabHeadersDelegate.

ios/chrome/browser/tabs/tab_headers_delegate.h

Index: ios/chrome/browser/tabs/tab_headers_delegate.h
diff --git a/ios/chrome/browser/tabs/tab_headers_delegate.h b/ios/chrome/browser/tabs/tab_headers_delegate.h
new file mode 100644
index 0000000000000000000000000000000000000000..d888494a90a773dd962f92bbd11170a6be4bec07
--- /dev/null
+++ b/ios/chrome/browser/tabs/tab_headers_delegate.h
@@ -0,0 +1,19 @@
+// Copyright 2017 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 IOS_CHROME_BROWSER_TABS_TAB_HEADERS_DELEGATE_H_
+#define IOS_CHROME_BROWSER_TABS_TAB_HEADERS_DELEGATE_H_
+
+#import <UIKit/UIKit.h>
+
+// A protocol implemented by a delegate of Tab that handles the headers above a
+// tab.
+@protocol TabHeadersDelegate
+
+// Called to retrieve the height of the header view above |tab|.
+- (CGFloat)headerHeightForTab:(Tab*)tab;
+
+@end
+
+#endif  // IOS_CHROME_BROWSER_TABS_TAB_HEADERS_DELEGATE_H_