page cycler: Use buffer-cache priming code on all systems.

base/file_util.h

Index: base/file_util.h
diff --git a/base/file_util.h b/base/file_util.h
index 64a91eea09a765124171d3683d2600dabb1a93a9..e62b30e09f8490968641c569c91ebe87443a1a89 100644
--- a/base/file_util.h
+++ b/base/file_util.h
@@ -159,6 +159,8 @@ bool ContentsEqual(const FilePath& filename1,
 bool TextContentsEqual(const FilePath& filename1, const FilePath& filename2);
 
 // Read the file at |path| into |contents|, returning true on success.
+// |contents| may be NULL, in which case this function is useful for its
+// side effect of priming the disk cache.
 // Useful for unit tests.
 bool ReadFileToString(const FilePath& path, std::string* contents);