Remove new space allocation in optimizing compiler, use Symbols::FromConcat where appropriate

runtime/vm/scanner.cc

 // 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.
 
 #include "vm/scanner.h"
 
 #include "platform/assert.h"
 #include "vm/dart.h"
 #include "vm/flags.h"
 #include "vm/object.h"
@@ skipping 313 matching lines @@
       i++;
     }
   }
 
   // We did not read a keyword.
   current_token_.kind = Token::kIDENT;
   String& literal =
       String::ZoneHandle(Z, Symbols::New(source_, ident_pos, ident_length));
   if (ident_char0 == Library::kPrivateIdentifierStart) {
     // Private identifiers are mangled on a per library basis.
-    literal = String::Concat(literal, private_key_);
-    literal = Symbols::New(literal);
+    literal = Symbols::FromConcat(literal, private_key_);
   }
   current_token_.literal = &literal;
 }
 
 
 // Parse integer or double number literal of format:
 // NUMBER = INTEGER | DOUBLE
 // INTEGER = D+ | (("0x" | "0X") H+)
 // DOUBLE = ((D+ ["." D*]) | ("." D+)) [ EXPONENT ]
 // EXPONENT = ("e" | "E") ["+" | "-"] D+
@@ skipping 627 matching lines @@
     keywords_[i].keyword_symbol = &Symbols::Keyword(token);
 
     int ch = keywords_[i].keyword_chars[0] - 'a';
     if (keywords_char_offset_[ch] == Token::kNumKeywords) {
       keywords_char_offset_[ch] = i;
     }
   }
 }
 
 }  // namespace dart