Generate snapshot for dartj2s; use it in the SDK.

dart/utils/compiler/build_helper.dart

Index: dart/utils/compiler/build_helper.dart
diff --git a/dart/utils/compiler/build_helper.dart b/dart/utils/compiler/build_helper.dart
index 9e29f84f158dff6f35bd51dc5b8c3ebb1bc79955..6821599be2391dbd4ca322476179aecac9c1aad4 100644
--- a/dart/utils/compiler/build_helper.dart
+++ b/dart/utils/compiler/build_helper.dart
@@ -116,7 +116,14 @@ if test -t 1; then
     COLORS="--enable-diagnostic-colors"
   fi
 fi
-exec "\$BIN_DIR"/dart$options "\$BIN_DIR/$path" \$COLORS "\$@"
+
+unset SNAPSHOT
+if test -f "\$BIN_DIR/${path}.snapshot"; then
+  # TODO(ahe): Remove the following line when we are relatively sure it works.
+  echo Using snapshot "\$BIN_DIR/${path}.snapshot" 1>&2
+  SNAPSHOT="--use_script_snapshot=\$BIN_DIR/${path}.snapshot"

[dgrove, 2012/10/17 12:59:17]

you want quotes around \$BIN_DIR to deal with BIN_DIR containing spaces.

[ahe, 2012/10/17 13:03:07]

Actually, there are quotes around everything. That should be sufficient. But I
will test it.

+fi
+exec "\$BIN_DIR"/dart$options \$SNAPSHOT "\$BIN_DIR/$path" \$COLORS "\$@"
 ''',
 '''
 @echo off