Fix the snapshot_cache unittests.

ios/chrome/browser/snapshots/snapshot_cache_internal.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 IOS_CHROME_BROWSER_SNAPSHOTS_SNAPSHOT_CACHE_INTERNAL_H_
+#define IOS_CHROME_BROWSER_SNAPSHOTS_SNAPSHOT_CACHE_INTERNAL_H_
+
+#import "ios/chrome/browser/snapshots/snapshot_cache_internal.h"
+
+namespace base {
+class FilePath;
+}
+
+@class NSString;
+
+@interface SnapshotCache (Internal)
+// Returns filepath to the color snapshot of |sessionID|.
++ (base::FilePath)imagePathForSessionID:(NSString*)sessionID;
+// Returns filepath to the greyscale snapshot of |sessionID|.
++ (base::FilePath)greyImagePathForSessionID:(NSString*)sessionID;
+// Returns whether the snapshots are cached in a LRU cache.
+- (BOOL)usesLRUCache;
+// Returns whether the in-memory cache (as opposed to the on-disk cache) is
+// enabled.
+- (BOOL)inMemoryCacheIsEnabled;
+@end
+
+#endif  // IOS_CHROME_BROWSER_SNAPSHOTS_SNAPSHOT_CACHE_INTERNAL_H_