Expose thumbnails of pages to iOS share extensions.

ios/chrome/browser/ui/activity_services/chrome_activity_item_thumbnail_generator.h

Index: ios/chrome/browser/ui/activity_services/chrome_activity_item_thumbnail_generator.h
diff --git a/ios/chrome/browser/ui/activity_services/chrome_activity_item_thumbnail_generator.h b/ios/chrome/browser/ui/activity_services/chrome_activity_item_thumbnail_generator.h
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index 0000000000000000000000000000000000000000..4719091360861b784b485e7a748b9fa0a24e53b9
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+++ b/ios/chrome/browser/ui/activity_services/chrome_activity_item_thumbnail_generator.h
@@ -0,0 +1,23 @@
+// 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_UI_ACTIVITY_SERVICES_CHROME_ACTIVITY_ITEM_THUMBNAIL_GENERATOR_H_
+#define IOS_CHROME_BROWSER_UI_ACTIVITY_SERVICES_CHROME_ACTIVITY_ITEM_THUMBNAIL_GENERATOR_H_
+
+#import <CoreGraphics/CoreGraphics.h>
+#import <UIKit/UIKit.h>
+
+@class Tab;
+
+// Block returning a thumbnail at the specified size. May return nil.
+typedef UIImage* (^ThumbnailGeneratorBlock)(const CGSize&);
+
+namespace activity_services {
+
+// Returns a thumbnail generator for the tab |tab|.
+ThumbnailGeneratorBlock ThumbnailGeneratorForTab(Tab* tab);
+
+}  // namespace activity_services
+
+#endif  // IOS_CHROME_BROWSER_UI_ACTIVITY_SERVICES_CHROME_ACTIVITY_ITEM_THUMBNAIL_GENERATOR_H_