Add UMA to determine how often we offline a page with previews.

chrome/browser/loader/chrome_navigation_data.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_BROWSER_LOADER_CHROME_NAVIGATION_DATA_H_
 #define CHROME_BROWSER_LOADER_CHROME_NAVIGATION_DATA_H_
 
 #include <memory>
 
 #include "base/macros.h"
 #include "base/supports_user_data.h"
+#include "components/data_reduction_proxy/core/browser/data_reduction_proxy_data.h"

[RyanSturm, 2017/06/02 20:50:33]

Any reason for switching forward declare to header? Is it needed for the
std::move so that the destructor is declared?

[Pete Williamson, 2017/06/02 21:40:32]

It was a different compile error:
 error: invalid application of 'sizeof' to an incomplete type
'data_reduction_proxy::DataReductionProxyData'

 #include "content/public/browser/navigation_data.h"
-
-namespace data_reduction_proxy {
-class DataReductionProxyData;
-}
+#include "content/public/common/previews_state.h"
 
 namespace net {
 class URLRequest;
 }
 
 class ChromeNavigationData : public content::NavigationData,
                              public base::SupportsUserData::Data {
  public:
   ChromeNavigationData();
   ~ChromeNavigationData() override;
 
   // Creates a new ChromeNavigationData that is a deep copy of the original. Any
   // changes to the original after the clone is created will not be reflected in
   // the clone.
   // |data_reduction_proxy_data_| is deep copied.
   std::unique_ptr<content::NavigationData> Clone() const override;
 
   // Takes ownership of |data_reduction_proxy_data|.
   void SetDataReductionProxyData(
       std::unique_ptr<data_reduction_proxy::DataReductionProxyData>
           data_reduction_proxy_data) {
     data_reduction_proxy_data_ = std::move(data_reduction_proxy_data);
   }
 
   data_reduction_proxy::DataReductionProxyData* GetDataReductionProxyData()
       const {
     return data_reduction_proxy_data_.get();
   }
 
+  content::PreviewsState previews_state() { return previews_state_; }
+  void set_previews_state(content::PreviewsState previews_state) {
+    previews_state_ = previews_state;
+  }
+
   static ChromeNavigationData* GetDataAndCreateIfNecessary(
       net::URLRequest* request);
 
  private:
   // Manages the lifetime of optional DataReductionProxy information.
   std::unique_ptr<data_reduction_proxy::DataReductionProxyData>
       data_reduction_proxy_data_;
+  content::PreviewsState previews_state_;
 
   DISALLOW_COPY_AND_ASSIGN(ChromeNavigationData);
 };
 
 #endif  // CHROME_BROWSER_LOADER_CHROME_NAVIGATION_DATA_H_