Add seed value constructor to DataBuilder

This is needed for experimenting with alternate fuzzing frameworks
that can generate a seed value without needing to hash the input.

Change-Id: I8207fd16c83265268c7e5764b707456e59f79a07
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/67501
Commit-Queue: Ryan Harrison <rharrison@chromium.org>
Auto-Submit: Ryan Harrison <rharrison@chromium.org>
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>

fuzzers/data_builder.h

@@ -28,12 +28,16 @@ namespace fuzzers {
 /// Builder for generic pseudo-random data using a data buffer as seed
 class DataBuilder {
  public:
-  /// @brief Initialize random number generations
+  /// @brief Initialize internal random number generation using data as seed
   /// @param data - pointer to a data buffer to use as a seed
   /// @param size - size of data buffer
   explicit DataBuilder(const uint8_t* data, size_t size)
       : generator_(data, size) {}
 
+  /// @brief Initialize internal random number generation using seed value
+  /// @param seed - value to use as seed
+  explicit DataBuilder(uint64_t seed) : generator_(seed) {}
+
   ~DataBuilder() = default;
   DataBuilder(DataBuilder&&) = default;