Implement correct bigint to double conversion.

runtime/vm/bigint_operations.h

 // Copyright 2012 Google Inc. All Rights Reserved.
 
 #ifndef VM_BIGINT_OPERATIONS_H_
 #define VM_BIGINT_OPERATIONS_H_
 
 #include "platform/utils.h"
 
 #include "vm/object.h"
 
 namespace dart {
@@ skipping 48 matching lines @@
   static const char* ToDecimalCString(const Bigint& bigint,
                                       uword (*allocator)(intptr_t size));
 
   static bool FitsIntoSmi(const Bigint& bigint);
   static RawSmi* ToSmi(const Bigint& bigint);
 
   static bool FitsIntoMint(const Bigint& bigint);
   static int64_t ToMint(const Bigint& bigint);
 
   static bool FitsIntoUint64(const Bigint& bigint);
+  static bool AbsFitsIntoUint64(const Bigint& bigint);
   static uint64_t ToUint64(const Bigint& bigint);
   static uint64_t AbsToUint64(const Bigint& bigint);
 
   static RawDouble* ToDouble(const Bigint& bigint);
 
   static RawBigint* Add(const Bigint& a, const Bigint& b) {
     bool negate_b = false;
     return AddSubtract(a, b, negate_b);
   }
   static RawBigint* Subtract(const Bigint& a, const Bigint& b) {
@@ skipping 66 matching lines @@
   static RawBigint* Copy(const Bigint& bigint);
 
   static int CountBits(Chunk digit);
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(BigintOperations);
 };
 
 }  // namespace dart
 
 #endif  // VM_BIGINT_OPERATIONS_H_