Add macro so that gpu trace marker can add an arg to the TRACE_EVENT it makes

BUG=skia:
R=bsalomon@google.com

Author: egdaniel@google.com

Review URL: https://codereview.chromium.org/379223004
diff --git a/src/gpu/GrContext.cpp b/src/gpu/GrContext.cpp
index 85cc8cd..4e833a1 100755
--- a/src/gpu/GrContext.cpp
+++ b/src/gpu/GrContext.cpp
@@ -1226,7 +1226,7 @@
     GrDrawTarget* target = this->prepareToDraw(&paint, BUFFERED_DRAW, &are, &acf);
     GrDrawState* drawState = target->drawState();
 
-    GR_CREATE_TRACE_MARKER("GrContext::drawPath", target);
+    GR_CREATE_TRACE_MARKER1("GrContext::drawPath", target, "Is Convex", path.isConvex());
 
     const SkStrokeRec& strokeRec = strokeInfo.getStrokeRec();