SkRecord: infer return type for visit() and mutate().

tests/RecorderTest.cpp

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "Test.h"
 
 #include "SkPictureRecorder.h"
@@ skipping 13 matching lines @@
     Tally() { sk_bzero(&fHistogram, sizeof(fHistogram)); }
 
     template <typename T>
     void operator()(const T&) { ++fHistogram[T::kType]; }
 
     template <typename T>
     int count() const { return fHistogram[T::kType]; }
 
     void apply(const SkRecord& record) {
         for (int i = 0; i < record.count(); i++) {
-            record.visit<void>(i, *this);
+            record.visit(i, *this);
         }
     }
 
 private:
     int fHistogram[kRecordTypes];
 };
 
 DEF_TEST(Recorder, r) {
     SkRecord record;
     SkRecorder recorder(&record, 1920, 1080);
@@ skipping 56 matching lines @@
         recorder.drawImageRect(image, SkRect::MakeWH(100, 100), nullptr);
         REPORTER_ASSERT(reporter, !image->unique());
 
         Tally tally;
         tally.apply(record);
 
         REPORTER_ASSERT(reporter, 1 == tally.count<SkRecords::DrawImageRect>());
     }
     REPORTER_ASSERT(reporter, image->unique());
 }