Pull JS assignments into var initializer.

tests/compiler/dart2js/js_backend_cps_ir_basic_test.dart

 // Copyright (c) 2014, 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.
 // VMOptions=-DUSE_CPS_IR=true
 
 // Tests for basic functionality.
 
 library basic_tests;
 
 import 'js_backend_cps_ir.dart';
 
 const List<TestEntry> tests = const [
   const TestEntry(r"""
 main() {
   var e = 1;
   var l = [1, 2, 3];
   var m = {'s': 1};
 
   print('(' ')');
   print('(${true})');
   print('(${1})');
   print('(${[1, 2, 3]})');
   print('(${{'s': 1}})');
   print('($e)');
   print('($l)');
   print('($m)');
 }""",r"""
 function() {
-  var l, m;
-  l = [1, 2, 3];
-  m = P.LinkedHashMap_LinkedHashMap$_literal(["s", 1]);
+  var l = [1, 2, 3], m = P.LinkedHashMap_LinkedHashMap$_literal(["s", 1]);
   P.print("()");
   P.print("(" + true + ")");
   P.print("(" + 1 + ")");
   P.print("(" + H.S([1, 2, 3]) + ")");
   P.print("(" + H.S(P.LinkedHashMap_LinkedHashMap$_literal(["s", 1])) + ")");
   P.print("(" + 1 + ")");
   P.print("(" + H.S(l) + ")");
   P.print("(" + H.S(m) + ")");
   return null;
 }"""),
@@ skipping 32 matching lines @@
   a = b;
   b = t;
   print(a);
   print(b);
   print(b);
   print(foo(a));
 }
   """,
   """
 function() {
-  var a, b;
-  a = 10;
-  b = 1;
+  var a = 10, b = 1;
   P.print(b);
   P.print(a);
   P.print(a);
   P.print(V.foo(b));
   return null;
 }"""),
   const TestEntry(
   """
 foo() { return 42; }
 main() { return foo(); }
@@ skipping 58 matching lines @@
 function() {
   V.foo();
   return null;
 }"""),
   // Static setters
   const TestEntry("""
 var foo = 0;
 main() { print(foo = 42); }
 """, r"""
 function() {
-  var v0;
-  v0 = 42;
+  var v0 = 42;
   $.foo = v0;
   P.print(v0);
   return null;
 }"""),
   const TestEntry("""
 set foo(x) { print(x); }
 main() { foo = 42; }
 """, r"""
 function() {
   V.foo(42);
   return null;
 }""")
 ];
 
 
 void main() {
   runTests(tests);
 }