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

tools/DumpRecord.cpp

Index: tools/DumpRecord.cpp
diff --git a/tools/DumpRecord.cpp b/tools/DumpRecord.cpp
index e7d76f05155fe8ef6cff396b38a7fadceabb8403..efaf0eb58e81ea5fdee96fdefdc9a387b7e7d905 100644
--- a/tools/DumpRecord.cpp
+++ b/tools/DumpRecord.cpp
@@ -68,7 +68,7 @@ public:
 
             const SkRecord& record = *bp->record();
             for (int i = 0; i < record.count(); i++) {
-                record.visit<void>(i, *this);
+                record.visit(i, *this);
             }
 
             --fIndent;
@@ -119,6 +119,6 @@ void DumpRecord(const SkRecord& record,
                   bool timeWithCommand) {
     Dumper dumper(canvas, record.count(), timeWithCommand);
     for (int i = 0; i < record.count(); i++) {
-        record.visit<void>(i, dumper);
+        record.visit(i, dumper);
     }
 }