re2: Initialize sparse_to_dense_ on initial allocation under Valgrind.

third_party/re2/patches/sparse-array-valgrind.patch

+diff --git a/third_party/re2/util/sparse_array.h b/third_party/re2/util/sparse_array.h
+index 4ee5c94..7bc3a86 100644
+--- a/third_party/re2/util/sparse_array.h
++++ b/third_party/re2/util/sparse_array.h
+@@ -273,13 +273,13 @@ void SparseArray<Value>::resize(int new_max_size) {
+     int* a = new int[new_max_size];
+     if (sparse_to_dense_) {
+       memmove(a, sparse_to_dense_, max_size_*sizeof a[0]);
+-      // Don't need to zero the memory but appease Valgrind.
+-      if (valgrind_) {
+-        for (int i = max_size_; i < new_max_size; i++)
+-          a[i] = 0xababababU;
+-      }
+       delete[] sparse_to_dense_;
+     }
++    // Don't need to zero the memory but appease Valgrind.
++    if (valgrind_) {
++      for (int i = max_size_; i < new_max_size; i++)
++        a[i] = 0xababababU;
++    }
+     sparse_to_dense_ = a;
+ 
+     dense_.resize(new_max_size);