Adds logic to bump up the default heap for invoking dartc on Mac.

compiler/scripts/dartc_test.sh

 #!/bin/bash
 # Copyright (c) 2011, 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.
 
 case $(uname -s) in
     *Linux*|*linux*)
         OS="linux"
         ;;
     Darwin)
         OS="mac"
         ;;
     *)
         OS="generic"
         ;;
 esac
 
 SCRIPT_DIR=$(dirname $0)
 DARTC_HOME=$(dirname $SCRIPT_DIR)
 DARTC_LIBS=$DARTC_HOME/lib
 D8_EXEC=${D8_EXEC:-@D8_EXEC@}
 DART_SCRIPT_NAME=${DART_SCRIPT_NAME:-$(basename $0)}
 
 if [ -x /usr/libexec/java_home ]; then
   export JAVA_HOME=$(/usr/libexec/java_home -v '1.6+')
 fi
 
-exec java -ea -Dcom.google.dart.runner.d8="$D8_EXEC" \
+EXTRA_JVMARGS=
+OS=`uname | tr [A-Z] [a-z]`
+if [ "$OS" == "darwin" ] ; then
+  # Bump up the heap on Mac VMs
+  EXTRA_JVMARGS=-Xmx1024M
+fi
+
+exec java $EXTRA_JVMARGS $DART_JVMARGS -ea -Dcom.google.dart.runner.d8="$D8_EXEC" \
   -Dcom.google.dart.runner.progname="$DART_SCRIPT_NAME" \
   -classpath "@CLASSPATH@" \
   com.google.dart.runner.DartRunner $@