CC: Add 'cc-benchmark' traces for minimal tracing in benchmarks.

cc/output/software_renderer.cc

Index: cc/output/software_renderer.cc
diff --git a/cc/output/software_renderer.cc b/cc/output/software_renderer.cc
index a72df9dc0e3dfcfd90d6745c3b0669312c929bfd..1443f4dd297348dd32d3159de6ded9f44d51fab0 100644
--- a/cc/output/software_renderer.cc
+++ b/cc/output/software_renderer.cc
@@ -117,6 +117,7 @@ void SoftwareRenderer::FinishDrawingFrame(DrawingFrame* frame) {
 }
 
 void SoftwareRenderer::SwapBuffers(const CompositorFrameMetadata& metadata) {
+  TRACE_EVENT0("cc,cc-benchmark", "SoftwareRenderer::SwapBuffers");
   CompositorFrame compositor_frame;
   compositor_frame.metadata = metadata;
   compositor_frame.software_frame_data = current_frame_data_.Pass();