Move crypto_helpers from sync to base

base/rand_util.h

Index: base/rand_util.h
diff --git a/base/rand_util.h b/base/rand_util.h
index 4e902da2f356ea666098ca3d34b73518f418833a..ae97b474857e73c1c941dec03b5de221ae54c619 100644
--- a/base/rand_util.h
+++ b/base/rand_util.h
@@ -29,6 +29,10 @@ BASE_API uint64 RandGenerator(uint64 max);
 // Returns a random double in range [0, 1). Thread-safe.
 BASE_API double RandDouble();
 
+// fills |output_length| bytes of |output| with cryptographically strong random
+// data.
+BASE_API void RandBytes(void* output, size_t output_length);
+
 // Returns a random string of the specified length.
 BASE_API std::string RandBytesAsString(size_t length);