Use zone allocated C-strings instead of String heap objects to construct signature symbols

runtime/vm/symbols.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_SYMBOLS_H_
 #define VM_SYMBOLS_H_
 
+#include "vm/growable_array.h"
 #include "vm/object.h"
 #include "vm/snapshot_ids.h"
 
 namespace dart {
 
 // Forward declarations.
 class Isolate;
 class ObjectPointerVisitor;
 
 // One-character symbols are added implicitly.
@@ skipping 569 matching lines @@
   // Creates a new Symbol from an array of UTF-32 encoded characters.
   static RawString* FromUTF32(const int32_t* utf32_array, intptr_t len);
 
   static RawString* New(const String& str);
   static RawString* New(const String& str,
                         intptr_t begin_index,
                         intptr_t length);
 
   static RawString* FromConcat(const String& str1, const String& str2);
 
+  static RawString* FromConcatAll(const GrowableArray<const String*>& strs);
+
   // Returns char* of predefined symbol.
   static const char* Name(SymbolId symbol);
 
   static RawString* FromCharCode(int32_t char_code);
 
   static RawString** PredefinedAddress() {
     return reinterpret_cast<RawString**>(&predefined_);
   }
 
   static void DumpStats();
@@ skipping 31 matching lines @@
   friend class SnapshotReader;
   friend class SnapshotWriter;
   friend class ApiMessageReader;
 
   DISALLOW_COPY_AND_ASSIGN(Symbols);
 };
 
 }  // namespace dart
 
 #endif  // VM_SYMBOLS_H_