Only reload libraries when they may have been modified.

runtime/vm/bit_vector.cc

 // Copyright (c) 2012, 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.
 
 #include "vm/bit_vector.h"
 
 #include "vm/os.h"
 
 namespace dart {
 
@@ skipping 82 matching lines @@
 
 
 void BitVector::Intersect(const BitVector* other) {
   ASSERT(other->length() == length());
   for (intptr_t i = 0; i < data_length_; i++) {
     data_[i] = data_[i] & other->data_[i];
   }
 }
 
 
+bool BitVector::IsEmpty() const {
+  for (intptr_t i = 0; i < data_length_; i++) {
+    if (data_[i] != 0) {
+      return false;
+    }
+  }
+  return true;
+}
+
+
 void BitVector::Print() const {
   OS::Print("[");
   for (intptr_t i = 0; i < length_; i++) {
     OS::Print(Contains(i) ? "1" : "0");
   }
   OS::Print("]");
 }
 
 }  // namespace dart