- Do not read past the end of the utf32_array.

runtime/vm/object.cc

Index: runtime/vm/object.cc
===================================================================
--- runtime/vm/object.cc	(revision 15726)
+++ runtime/vm/object.cc	(working copy)
@@ -9996,16 +9996,17 @@
 bool String::Equals(const int32_t* utf32_array, intptr_t len) const {
   CodePointIterator it(*this);
   intptr_t i = 0;
-  while (it.Next()) {
-    if (it.Current() != static_cast<int32_t>(utf32_array[i])) {
+  bool has_more = it.Next();
+  while (has_more && (i < len)) {
+    if ((it.Current() != static_cast<int32_t>(utf32_array[i]))) {
       return false;
     }
+    // Advance both streams forward.
     ++i;
+    has_more = it.Next();
   }
-  if (i != len) {
-    return false;
-  }
-  return true;
+  // Strings are only true iff we reached the end in both streams.
+  return (i == len) && !has_more;
 }