Fix some more shorten-64-to-32 warnings:

runtime/platform/utils.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_UTILS_H_
 #define PLATFORM_UTILS_H_
 
 #include "platform/assert.h"
 #include "platform/globals.h"
 
@@ skipping 186 matching lines @@
   static uint16_t HostToLittleEndian16(uint16_t host_value);
   static uint32_t HostToLittleEndian32(uint32_t host_value);
   static uint64_t HostToLittleEndian64(uint64_t host_value);
 
   static bool DoublesBitEqual(const double a, const double b) {
     return bit_cast<int64_t, double>(a) == bit_cast<int64_t, double>(b);
   }
 
   // dart2js represents integers as double precision floats, which can
   // represent anything in the range -2^53 ... 2^53.
-  static bool IsJavascriptInt64(int64_t value) {
+  static bool IsJavascriptInt(int64_t value) {
     return ((-0x20000000000000LL <= value) && (value <= 0x20000000000000LL));
   }
-  static bool IsJavascriptInt(intptr_t value) {
-#if defined(ARCH_IS_64BIT)
-    return ((-0x20000000000000LL <= value) && (value <= 0x20000000000000LL));
-#else
-    return true;
-#endif
-  }
 
   static char* StrError(int err, char* buffer, size_t bufsize);
 };
 
 }  // namespace dart
 
 #if defined(TARGET_OS_ANDROID)
 #include "platform/utils_android.h"
 #elif defined(TARGET_OS_LINUX)
 #include "platform/utils_linux.h"
 #elif defined(TARGET_OS_MACOS)
 #include "platform/utils_macos.h"
 #elif defined(TARGET_OS_WINDOWS)
 #include "platform/utils_win.h"
 #else
 #error Unknown target os.
 #endif
 
 #endif  // PLATFORM_UTILS_H_