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

tests/RecordTestUtils.h

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef RecordTestUtils_DEFINED
 #define RecordTestUtils_DEFINED
 
@@ skipping 12 matching lines @@
     void operator()(const U& r) { ptr = &r; type = U::kType; }
 
     template <typename T>
     void operator()(const T&) { type = U::kType; }
 };
 
 // Assert that the ith command in record is of type T, and return it.
 template <typename T>
 static const T* assert_type(skiatest::Reporter* r, const SkRecord& record, int index) {
     ReadAs<T> reader;
-    record.visit<void>(index, reader);
+    record.visit(index, reader);
     REPORTER_ASSERT(r, T::kType == reader.type);
     REPORTER_ASSERT(r, SkToBool(reader.ptr));
     return reader.ptr;
 }
 
 template <typename DrawT> struct MatchType {
     template <typename T> int operator()(const T&) { return 0; }
     int operator()(const DrawT&) { return 1; }
 };
 
 template <typename DrawT> int count_instances_of_type(const SkRecord& record) {
     MatchType<DrawT> matcher;
     int counter = 0;
     for (int i = 0; i < record.count(); i++) {
-        counter += record.visit<int>(i, matcher);
+        counter += record.visit(i, matcher);
     }
     return counter;
 }
 
 template <typename DrawT> int find_first_instances_of_type(const SkRecord& record) {
     MatchType<DrawT> matcher;
     for (int i = 0; i < record.count(); i++) {
-        if (record.visit<int>(i, matcher)) {
+        if (record.visit(i, matcher)) {
             return i;
         }
     }
     return -1;
 }
 
 #endif//RecordTestUtils_DEFINED