Fix config strings in nanobench tracing

These are transient, so need to be copied.

Bug: skia:
Change-Id: Id24db0b96f343ecd034dd015da6e19ea61579b56
Reviewed-on: https://skia-review.googlesource.com/41741
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>

bench/nanobench.cpp

@@ -1273,7 +1273,7 @@ int main(int argc, char** argv) {
                 }
             }
 
-            TRACE_EVENT1("skia", bench->getUniqueName(), "config", config);
+            TRACE_EVENT1("skia", bench->getUniqueName(), "config", TRACE_STR_COPY(config));
 
             target->setup();
             bench->perCanvasPreDraw(canvas);