Improve gpu tracing when applying markers directly to gpu target

src/gpu/gl/GrGpuGL.cpp

Index: src/gpu/gl/GrGpuGL.cpp
diff --git a/src/gpu/gl/GrGpuGL.cpp b/src/gpu/gl/GrGpuGL.cpp
index 2eb76a5aff43137e69a0d2461efa0f2a1ec0ffb9..eddccc39f67e626a0beb814cd4016a5ce6e8bf0b 100644
--- a/src/gpu/gl/GrGpuGL.cpp
+++ b/src/gpu/gl/GrGpuGL.cpp
@@ -2982,7 +2982,7 @@ bool GrGpuGL::onCanCopySurface(GrSurface* dst,
 void GrGpuGL::didAddGpuTraceMarker() {
     if (this->caps()->gpuTracingSupport()) {
         const GrTraceMarkerSet& markerArray = this->getActiveTraceMarkers();
-        SkString markerString = markerArray.toString();
+        SkString markerString = markerArray.toStringLast();
         GL_CALL(PushGroupMarker(0, markerString.c_str()));
     }
 }