Support StackTrace.current

tool/input_sdk/lib/core/stacktrace.dart

Index: tool/input_sdk/lib/core/stacktrace.dart
diff --git a/tool/input_sdk/lib/core/stacktrace.dart b/tool/input_sdk/lib/core/stacktrace.dart
index ef8cc4dbb4adfac17f33fef5f28d31fe15d45a2c..a3b7a4f2e9395b9d0ef395296bb9c72bfd67fa28 100644
--- a/tool/input_sdk/lib/core/stacktrace.dart
+++ b/tool/input_sdk/lib/core/stacktrace.dart
@@ -15,6 +15,18 @@ part of dart.core;
  */
 abstract class StackTrace {
   /**
+   * Returns a representation of the current stack trace.
+   *
+   * This is similar to what can be achieved by doing:
+   *
+   *     try { throw 0; } catch (_, stack) { return stack; }
+   *
+   * The getter achieves this without throwing, except on platforms that
+   * have no other way to get a stack trace.
+   */
+  external static StackTrace get current;
+
+  /**
    * Returns a [String] representation of the stack trace.
    *
    * The string represents the full stack trace starting from