Testable patch parser.

dart/sdk/lib/_internal/compiler/implementation/patch_parser.dart

Index: dart/sdk/lib/_internal/compiler/implementation/patch_parser.dart
diff --git a/dart/sdk/lib/_internal/compiler/implementation/patch_parser.dart b/dart/sdk/lib/_internal/compiler/implementation/patch_parser.dart
index 41e937f2a0747653f0b4ae790d29e8ca303e3de0..2c103acc68209b54f3063a731cba31515d050a2f 100644
--- a/dart/sdk/lib/_internal/compiler/implementation/patch_parser.dart
+++ b/dart/sdk/lib/_internal/compiler/implementation/patch_parser.dart
@@ -329,15 +329,18 @@ class PatchElementListener extends ElementListener implements PatchListener {
 
   void pushElement(Element patch) {
     if (isMemberPatch || (isClassPatch && patch is ClassElement)) {
-      // Apply patch.
       patch.addMetadata(popMetadata());
-      LibraryElement originLibrary = compilationUnitElement.getLibrary();
-      assert(originLibrary.isPatched);
-      Element origin = originLibrary.localLookup(patch.name);
-      _patchElement(listener, origin, patch);
+      applyPatch(patch);
     }
     super.pushElement(patch);
   }
+
+  void applyPatch(Element patch) {
+    LibraryElement originLibrary = compilationUnitElement.getLibrary();
+    assert(originLibrary.isPatched);
+    Element origin = originLibrary.localLookup(patch.name);
+    _patchElement(listener, origin, patch);
+  }
 }
 
 /**
@@ -390,6 +393,12 @@ class PatchMetadataAnnotation extends MetadataAnnotationX {
   Token get beginToken => null;
 }
 
+void patchElement(leg.DiagnosticListener listener,
+                  Element origin,
+                  Element patch) {
+  _patchElement(listener, origin, patch);
+}
+
 void _patchElement(leg.DiagnosticListener listener,
                    Element origin,
                    Element patch) {
@@ -589,3 +598,5 @@ bool _isPatchElement(Element element) {
   }
   return false;
 }
+
+bool isPatchElement(Element element) => _isPatchElement(element);