Precompilation: compact the symbol table.

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"
@@ skipping 554 matching lines @@
 
   // Add all the symbols that were cached in the VM isolate to this isolate,
   // we do this when an Isolate is not created from the snapshot so that
   // we get a unified symbol table that can be be dumped into the VM isolate
   // snapshot.
   static void AddPredefinedSymbolsToIsolate();
 
   // Initialize and setup a symbol table for the isolate.
   static void SetupSymbolTable(Isolate* isolate);
 
+  // Treat the symbol table as weak and collect garbage. Answer the number of
+  // freed symbols.

[siva, 2016/01/27 21:21:10]

Maybe

"Returns the number of symbols that have been deleted from the symbol table as
they are not referenced anywhere."

[rmacnak, 2016/01/27 23:06:20]

Done.

+  static intptr_t Compact(Isolate* isolate);
+
   // Creates a Symbol given a C string that is assumed to contain
   // UTF-8 encoded characters and '\0' is considered a termination character.
   // TODO(7123) - Rename this to FromCString(....).
   static RawString* New(const char* cstr) {
     return New(cstr, strlen(cstr));
   }
   static RawString* New(const char* cstr, intptr_t length);
 
   // Creates a new Symbol from an array of UTF-8 encoded characters.
   static RawString* FromUTF8(const uint8_t* utf8_array, intptr_t len);
@@ skipping 72 matching lines @@
   friend class SnapshotReader;
   friend class SnapshotWriter;
   friend class ApiMessageReader;
 
   DISALLOW_COPY_AND_ASSIGN(Symbols);
 };
 
 }  // namespace dart
 
 #endif  // VM_SYMBOLS_H_