Move dart2js from sdk/lib/_internal/compiler to pkg/compiler

sdk/bin/dart2js_sdk

 #!/bin/bash
 # 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.
 
 function follow_links() {
   file="$1"
   while [ -h "$file" ]; do
     # On Mac OS, readlink -f doesn't work.
     file="$(readlink "$file")"
   done
   echo "$file"
 }
 
 # Unlike $0, $BASH_SOURCE points to the absolute path of this file.
 PROG_NAME="$(follow_links "$BASH_SOURCE")"
 
 # Handle the case where dart-sdk/bin has been symlinked to.
 BIN_DIR="$(cd "${PROG_NAME%/*}" ; pwd -P)"
 
 SDK_DIR="$(cd "${BIN_DIR}/.." ; pwd -P)"
 
-DART2JS="$SDK_DIR/lib/_internal/compiler/implementation/dart2js.dart"
-
 DART="$BIN_DIR/dart"
 
 SNAPSHOT_DIR="$BIN_DIR/snapshots"
 SNAPSHOT="$SNAPSHOT_DIR/dart2js.dart.snapshot"
 
 unset EXTRA_OPTIONS
 declare -a EXTRA_OPTIONS
 
 if test -t 1; then
   # Stdout is a terminal.
@@ skipping 21 matching lines @@
     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
-  exec "$DART" "${EXTRA_VM_OPTIONS[@]}" "$DART2JS" "${EXTRA_OPTIONS[@]}" "$@"
-fi
+exec "$DART" "${EXTRA_VM_OPTIONS[@]}" "$SNAPSHOT" "${EXTRA_OPTIONS[@]}" "$@"