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

tests/RecordTest.cpp

Index: tests/RecordTest.cpp
diff --git a/tests/RecordTest.cpp b/tests/RecordTest.cpp
index e613b425fdc7f607d580c053bc7b028819d5c8fb..1b4077cce8a291d482bdfeaf97fd99879bb946c4 100644
--- a/tests/RecordTest.cpp
+++ b/tests/RecordTest.cpp
@@ -29,7 +29,7 @@ public:
 
     void apply(const SkRecord& record) {
         for (int i = 0; i < record.count(); i++) {
-            record.visit<void>(i, *this);
+            record.visit(i, *this);
         }
     }
 
@@ -47,7 +47,7 @@ struct Stretch {
 
     void apply(SkRecord* record) {
         for (int i = 0; i < record->count(); i++) {
-            record->mutate<void>(i, *this);
+            record->mutate(i, *this);
         }
     }
 };