Use official JSON encoding for stream

runtime/vm/unicode.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 VM_UNICODE_H_
 #define VM_UNICODE_H_
 
 #include "vm/allocation.h"
 #include "vm/globals.h"
 
@@ skipping 99 matching lines @@
 
 
 class Utf16 : AllStatic {
  public:
   // Returns the length of the code point in UTF-16 code units.
   static intptr_t Length(int32_t ch) {
     return (ch <= Utf16::kMaxCodeUnit) ? 1 : 2;
   }
 
   // Returns true if ch is a lead or trail surrogate.
-  static bool IsSurrogate(int32_t ch) {
+  static bool IsSurrogate(uint32_t ch) {
     return (ch & 0xFFFFF800) == 0xD800;
   }
 
   // Returns true if ch is a lead surrogate.
-  static bool IsLeadSurrogate(int32_t ch) {
+  static bool IsLeadSurrogate(uint32_t ch) {
     return (ch & 0xFFFFFC00) == 0xD800;
   }
 
   // Returns true if ch is a low surrogate.
-  static bool IsTrailSurrogate(int32_t ch) {
+  static bool IsTrailSurrogate(uint32_t ch) {
     return (ch & 0xFFFFFC00) == 0xDC00;
   }
 
   // Returns the character at i and advances i to the next character
   // boundary.
   static int32_t Next(const uint16_t* characters, intptr_t* i, intptr_t len) {
     int32_t ch = characters[*i];
     if (Utf16::IsLeadSurrogate(ch) && (*i < (len - 1))) {
       int32_t ch2 = characters[*i + 1];
       if (Utf16::IsTrailSurrogate(ch2)) {
         ch = Utf16::Decode(ch, ch2);
         *i += 1;
       }
     }
     *i += 1;
     return ch;
   }
 
   // Decodes a surrogate pair into a supplementary code point.
-  static int32_t Decode(int32_t lead, int32_t trail) {
-    return 0x10000 + ((lead & 0x3FF) << 10) + (trail & 0x3FF);
+  static int32_t Decode(uint16_t lead, uint16_t trail) {
+    return 0x10000 + ((lead & 0x000003FF) << 10) + (trail & 0x3FF);
   }
 
   // Encodes a single code point.
   static void Encode(int32_t codepoint, uint16_t* dst);
 
   static const int32_t kMaxCodeUnit = 0xFFFF;
 
  private:
   static const int32_t kLeadSurrogateOffset = (0xD800 - (0x10000 >> 10));
 
@@ skipping 60 matching lines @@
   // Data for small code points with one mapping
   static const int16_t stage2_[];
 
   // Data for large code points or code points with both mappings.
   static const int32_t stage2_exception_[][2];
 };
 
 }  // namespace dart
 
 #endif  // VM_UNICODE_H_