Fix some errors from UBSan.

runtime/vm/weak_table.h

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef VM_WEAK_TABLE_H_
 #define VM_WEAK_TABLE_H_
 
 #include "vm/globals.h"
 
 #include "platform/assert.h"
@@ skipping 136 matching lines @@
     if (val == 0) {
       data_[ObjectIndex(i)] = kDeletedEntry;
       set_count(count() - 1);
     }
     data_[ValueIndex(i)] = val;
   }
 
   void Rehash();
 
   static intptr_t Hash(RawObject* key) {
-    return reinterpret_cast<intptr_t>(key) * 92821;
+    return reinterpret_cast<uintptr_t>(key) * 92821;
   }
 
   // data_ contains size_ tuples of key/value.
   intptr_t* data_;
   // size_ keeps the number of entries in data_. used_ maintains the number of
   // non-NULL entries and will trigger rehashing if needed. count_ stores the
   // number valid entries, and will determine the size_ after rehashing.
   intptr_t size_;
   intptr_t used_;
   intptr_t count_;
 
   DISALLOW_COPY_AND_ASSIGN(WeakTable);
 };
 
 }  // namespace dart
 
 #endif  // VM_WEAK_TABLE_H_