Export all CWV* symbols from the ios/web_view dynamic library.

ios/web_view/public/cwv_html_element.h

 // 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_WEB_VIEW_PUBLIC_CWV_HTML_ELEMENT_H_
 #define IOS_WEB_VIEW_PUBLIC_CWV_HTML_ELEMENT_H_
 
 #import <Foundation/Foundation.h>
 
+#if defined(CWV_IMPLEMENTATION)
+#include "ios/web_view/public/cwv_export.h"
+#else
+#include <ChromeWebView/cwv_export.h>
+#endif
+
 // Encapsulates information about HTML element. Used in
 // delegate methods.
-@interface CWVHTMLElement : NSObject
+CWV_EXPORT @interface CWVHTMLElement : NSObject
 
 // |href| property of an HTML element.
 @property(nullable, copy, readonly) NSURL* hyperlink;
 // |src| property of an HTML element.
 @property(nullable, copy, readonly) NSURL* mediaSource;
 // |innerText| property of an HTML element.
 @property(nullable, copy, readonly) NSString* text;
 @end
 
 #endif  // IOS_WEB_VIEW_PUBLIC_CWV_HTML_ELEMENT_H_