Revert change to Platform.excutable and add Platform.resolvedExecutable

sdk/lib/io/platform_impl.dart

Index: sdk/lib/io/platform_impl.dart
diff --git a/sdk/lib/io/platform_impl.dart b/sdk/lib/io/platform_impl.dart
index 3883957ef0d8129db4a47323b5f8ffd7a0038a81..6380e0d7c92f622495d3c9ca2149db2baafdfda9 100644
--- a/sdk/lib/io/platform_impl.dart
+++ b/sdk/lib/io/platform_impl.dart
@@ -10,6 +10,7 @@ class _Platform {
   external static String _operatingSystem();
   external static _localHostname();
   external static _executable();
+  external static _resolvedExecutable();
   /**
    * Retrieve the entries of the process environment.
    *
@@ -31,6 +32,7 @@ class _Platform {
   external static String _version();
 
   static String executable = _executable();
+  static String resolvedExecutable = _resolvedExecutable();
   static String packageRoot = _packageRoot();
 
   // Cache the OS environemnt. This can be an OSError instance if