Mark empty HashMap constructor as NoThrows.

sdk/lib/_internal/compiler/js_lib/collection_patch.dart

Index: sdk/lib/_internal/compiler/js_lib/collection_patch.dart
diff --git a/sdk/lib/_internal/compiler/js_lib/collection_patch.dart b/sdk/lib/_internal/compiler/js_lib/collection_patch.dart
index 78147f8871f13771f89f8f311f881f7b9021a51e..d71139369ef01dff614072c03a8d8f6becb61957 100644
--- a/sdk/lib/_internal/compiler/js_lib/collection_patch.dart
+++ b/sdk/lib/_internal/compiler/js_lib/collection_patch.dart
@@ -4,7 +4,7 @@
 
 // Patch file for dart:collection classes.
 import 'dart:_foreign_helper' show JS;
-import 'dart:_js_helper' show fillLiteralMap, NoInline, patch;
+import 'dart:_js_helper' show fillLiteralMap, NoInline, NoThrows, patch;
 
 @patch
 class HashMap<K, V> {
@@ -523,7 +523,7 @@ class LinkedHashMap<K, V> {
   }
 
   // Private factory constructor called by generated code for map literals.
-  @NoInline()
+  @NoThrows() @NoInline()
   factory LinkedHashMap._empty() {
     return new _LinkedHashMap<K, V>();
   }