Add a priority to source changes for assists and fixes

pkg/analyzer_plugin/test/integration/support/protocol_matchers.dart

Index: pkg/analyzer_plugin/test/integration/support/protocol_matchers.dart
diff --git a/pkg/analyzer_plugin/test/integration/support/protocol_matchers.dart b/pkg/analyzer_plugin/test/integration/support/protocol_matchers.dart
index 5c4d7933af9caf171dc0bf58b4540f4951bae58c..6f0b2c48c34be783863867a536f84fea909b2f53 100644
--- a/pkg/analyzer_plugin/test/integration/support/protocol_matchers.dart
+++ b/pkg/analyzer_plugin/test/integration/support/protocol_matchers.dart
@@ -331,12 +331,12 @@ final Matcher isEditGetAssistsParams = new LazyMatcher(() => new MatchesJsonObje
  * edit.getAssists result
  *
  * {
- *   "assists": List<SourceChange>
+ *   "assists": List<PrioritizedSourceChange>
  * }
  */
 final Matcher isEditGetAssistsResult = new LazyMatcher(() => new MatchesJsonObject(
   "edit.getAssists result", {
-    "assists": isListOf(isSourceChange)
+    "assists": isListOf(isPrioritizedSourceChange)
   }));
 
 /**
@@ -483,13 +483,13 @@ final Matcher isAnalysisError = new LazyMatcher(() => new MatchesJsonObject(
  *
  * {
  *   "error": AnalysisError
- *   "fixes": List<SourceChange>
+ *   "fixes": List<PrioritizedSourceChange>
  * }
  */
 final Matcher isAnalysisErrorFixes = new LazyMatcher(() => new MatchesJsonObject(
   "AnalysisErrorFixes", {
     "error": isAnalysisError,
-    "fixes": isListOf(isSourceChange)
+    "fixes": isListOf(isPrioritizedSourceChange)
   }));
 
 /**
@@ -1117,6 +1117,20 @@ final Matcher isPosition = new LazyMatcher(() => new MatchesJsonObject(
   }));
 
 /**
+ * PrioritizedSourceChange
+ *
+ * {
+ *   "priority": int
+ *   "change": SourceChange
+ * }
+ */
+final Matcher isPrioritizedSourceChange = new LazyMatcher(() => new MatchesJsonObject(
+  "PrioritizedSourceChange", {
+    "priority": isInt,
+    "change": isSourceChange
+  }));
+
+/**
  * RefactoringFeedback
  *
  * {