FuzzedDataProvider: Include the right headers for CHAR_BIT and memcpy

This fixes the build with libstdc++ after c416f80a ("Refactor
base::FuzzedDataProvider and fix the calling sites"):

* CHAR_BIT is part of limits.h (or <climits>), not the C++ <limits> header
* std::memcpy() needs <cstring>

Bug: 819294
Change-Id: I71439bd56c68fb7600a816ce03a71711ccfb00db
Reviewed-on: https://chromium-review.googlesource.com/c/1352320Reviewed-by: Max Moroz <mmoroz@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Raphael Kubo da Costa <raphael.kubo.da.costa@intel.com>
Cr-Commit-Position: refs/heads/master@{#611598}

base/test/fuzzed_data_provider.h

@@ -5,11 +5,12 @@
 #ifndef BASE_TEST_FUZZED_DATA_PROVIDER_H_
 #define BASE_TEST_FUZZED_DATA_PROVIDER_H_
 
+#include <limits.h>
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
-#include <limits>
+#include <cstring>
 #include <string>
 #include <utility>
 #include <vector>