Only report number of retained methods if we actually find an import of mirrors.

sdk/lib/_internal/compiler/implementation/js_backend/backend.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of js_backend;
 
 const VERBOSE_OPTIMIZER_HINTS = false;
 
 class JavaScriptItemCompilationContext extends ItemCompilationContext {
   final Set<HInstruction> boundsChecked = new Set<HInstruction>();
@@ skipping 1175 matching lines @@
    */
   String assembleCode(Element element) {
     assert(invariant(element, element.isDeclaration));
     return jsAst.prettyPrint(generatedCode[element], compiler).getText();
   }
 
   void assembleProgram() {
     emitter.assembleProgram();
     int totalMethodCount = generatedCode.length;
     if (totalMethodCount != preMirrorsMethodCount) {
-      int mirrorCount = totalMethodCount - preMirrorsMethodCount;
-      double percentage = (mirrorCount / totalMethodCount) * 100;
-      compiler.reportHint(
-          compiler.mainApp, MessageKind.MIRROR_BLOAT,
-          {'count': mirrorCount,
-           'total': totalMethodCount,
-           'percentage': percentage.round()});
+      bool reportedHint = false;
       for (LibraryElement library in compiler.libraries.values) {
         if (library.isInternalLibrary) continue;
         for (LibraryTag tag in library.tags) {
           Import importTag = tag.asImport();
           if (importTag == null) continue;
           LibraryElement importedLibrary = library.getLibraryFromTag(tag);
           if (importedLibrary != compiler.mirrorsLibrary) continue;
+          if (!reportedHint) {
+            reportedHint = true;
+            int mirrorCount = totalMethodCount - preMirrorsMethodCount;
+            double percentage = (mirrorCount / totalMethodCount) * 100;
+            compiler.reportHint(
+                compiler.mainApp, MessageKind.MIRROR_BLOAT,
+                {'count': mirrorCount,
+                 'total': totalMethodCount,
+                 'percentage': percentage.round()});
+          }
           MessageKind kind =
               compiler.mirrorUsageAnalyzerTask.hasMirrorUsage(library)
               ? MessageKind.MIRROR_IMPORT
               : MessageKind.MIRROR_IMPORT_NO_USAGE;
           compiler.withCurrentElement(library, () {
             compiler.reportInfo(importTag, kind);
           });
         }
       }
     }
@@ skipping 697 matching lines @@
     copy(constant.values);
     copy(constant.protoValue);
     copy(constant);
   }
 
   void visitConstructed(ConstructedConstant constant) {
     copy(constant.fields);
     copy(constant);
   }
 }