Patch re2 to support MSan.

third_party/re2/util/sparse_set.h

Index: third_party/re2/util/sparse_set.h
diff --git a/third_party/re2/util/sparse_set.h b/third_party/re2/util/sparse_set.h
index 165dd090eb49df4fc4a96259eb707d2d8a2370c7..f59ed0b031ea3f104421a05f186be267f4e3100e 100644
--- a/third_party/re2/util/sparse_set.h
+++ b/third_party/re2/util/sparse_set.h
@@ -54,13 +54,24 @@ namespace re2 {
 class SparseSet {
  public:
   SparseSet()
-    : size_(0), max_size_(0), sparse_to_dense_(NULL), dense_(NULL), valgrind_(RunningOnValgrind()) {}
+    : size_(0), max_size_(0), sparse_to_dense_(NULL), dense_(NULL),
+#if defined(MEMORY_SANITIZER)
+      valgrind_(true)
+#else
+      valgrind_(RunningOnValgrind())
+#endif
+  {
+  }
 
   SparseSet(int max_size) {
     max_size_ = max_size;
     sparse_to_dense_ = new int[max_size];
     dense_ = new int[max_size];
+#if defined(MEMORY_SANITIZER)
+    valgrind_ = true;
+#else
     valgrind_ = RunningOnValgrind();
+#endif
     // Don't need to zero the memory, but do so anyway
     // to appease Valgrind.
     if (valgrind_) {