Canonicalize uris in C++ instead of Dart for the standalone embedder.

runtime/vm/zone.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_ZONE_H_
 #define VM_ZONE_H_
 
 #include "platform/utils.h"
 #include "vm/allocation.h"
 #include "vm/handles.h"
@@ skipping 27 matching lines @@
   //
   // It is preferred to use Alloc<T>() instead, as that function can
   // check for integer overflow.  If you use AllocUnsafe, you are
   // responsible for avoiding integer overflow yourself.
   inline uword AllocUnsafe(intptr_t size);
 
 
   // Make a copy of the string in the zone allocated area.
   char* MakeCopyOfString(const char* str);
 
+  // Make a copy of the first n characters of a string in the zone
+  // allocated area.
+  char* MakeCopyOfStringN(const char* str, intptr_t len);
+
   // Concatenate strings |a| and |b|. |a| may be NULL. If |a| is not NULL,
   // |join| will be inserted between |a| and |b|.
   char* ConcatStrings(const char* a, const char* b, char join = ',');
 
   // TODO(zra): Remove these calls and replace them with calls to OS::SCreate
   // and OS::VSCreate.
   // These calls are deprecated. Do not add further calls to these functions.
   // instead use OS::SCreate and OS::VSCreate.
   // Make a zone-allocated string based on printf format and args.
   char* PrintToString(const char* format, ...) PRINTF_ATTRIBUTE(2, 3);
@@ skipping 223 matching lines @@
     memmove(reinterpret_cast<void*>(new_data),
             reinterpret_cast<void*>(old_data),
             old_len * kElementSize);
   }
   return new_data;
 }
 
 }  // namespace dart
 
 #endif  // VM_ZONE_H_