Add support for passing in vm options to the dart2js scripts.

sdk/bin/dart2js

Index: sdk/bin/dart2js
===================================================================
--- sdk/bin/dart2js	(revision 27645)
+++ sdk/bin/dart2js	(working copy)
@@ -33,7 +33,7 @@
   # Stdout is a terminal.
   if test 8 -le `tput colors`; then
     # Stdout has at least 8 colors, so enable colors.
-    EXTRA_OPTIONS[${#EXTRA_OPTIONS[@]}]='--enable-diagnostic-colors'
+    EXTRA_OPTIONS+=('--enable-diagnostic-colors')
   fi
 fi
 
@@ -41,7 +41,7 @@
 declare -a EXTRA_VM_OPTIONS
 
 if test -f "$SNAPSHOT"; then
-  EXTRA_OPTIONS[${#EXTRA_OPTIONS[@]}]="--library-root=$SDK_DIR"
+  EXTRA_OPTIONS+=("--library-root=$SDK_DIR")
 fi
 
 # Tell the VM to grow the heap more aggressively. This should only
@@ -52,10 +52,16 @@
 
 case $0 in
   *_developer)
-    EXTRA_VM_OPTIONS[${#EXTRA_VM_OPTIONS[@]}]='--checked'
+    EXTRA_VM_OPTIONS+=('--checked')
     ;;
 esac
 
+# We allow extra vm options to be passed in through an environment variable.
+if [[ $DART_VM_OPTIONS ]]; then
+  read -a OPTIONS <<< "$DART_VM_OPTIONS"
+  EXTRA_VM_OPTIONS+=("${OPTIONS[@]}")
+fi
+
 if test -f "$SNAPSHOT"; then
   exec "$DART" "${EXTRA_VM_OPTIONS[@]}" "$SNAPSHOT" "${EXTRA_OPTIONS[@]}" "$@"
 else