Avoid integer overflow when computing the size of new space in bytes.

runtime/platform/globals.h

 // 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.
 
 #ifndef PLATFORM_GLOBALS_H_
 #define PLATFORM_GLOBALS_H_
 
 // __STDC_FORMAT_MACROS has to be defined before including <inttypes.h> to
 // enable platform independent printf format specifiers.
 #ifndef __STDC_FORMAT_MACROS
@@ skipping 149 matching lines @@
 const int kWordSizeLog2 = 3;
 const uword kUwordMax = kMaxUint64;
 #endif
 
 // Bit sizes.
 const int kBitsPerByte = 8;
 const int kBitsPerByteLog2 = 3;
 const int kBitsPerWord = kWordSize * kBitsPerByte;
 
 // System-wide named constants.
-const int KB = 1024;
-const int MB = KB * KB;
-const int GB = KB * KB * KB;
+const intptr_t KB = 1024;
+const intptr_t MB = KB * KB;
+const intptr_t GB = KB * KB * KB;
 const intptr_t kIntptrOne = 1;
 const intptr_t kIntptrMin = (kIntptrOne << (kBitsPerWord - 1));
 const intptr_t kIntptrMax = ~kIntptrMin;
 
 // Time constants.
 const int kMillisecondsPerSecond = 1000;
 const int kMicrosecondsPerMillisecond = 1000;
 const int kMicrosecondsPerSecond = (kMicrosecondsPerMillisecond *
                                     kMillisecondsPerSecond);
 const int kNanosecondsPerMicrosecond = 1000;
@@ skipping 178 matching lines @@
 // have an implicit 'this' argument, the arguments of such methods
 // should be counted from two, not one."
 //
 #define PRINTF_ATTRIBUTE(string_index, first_to_check) \
   __attribute__((__format__(__printf__, string_index, first_to_check)))
 #else
 #define PRINTF_ATTRIBUTE(string_index, first_to_check)
 #endif
 
 #endif  // PLATFORM_GLOBALS_H_