Conditionally bail out earlier in Heap::reportMemoryUsageForTracing()

R=haraken
BUG=474470

Review URL: https://codereview.chromium.org/1301463002

git-svn-id: svn://svn.chromium.org/blink/trunk@200608 bbb929c8-8fbe-4397-9dbb-9b2b20218538
diff --git a/third_party/WebKit/Source/platform/heap/Heap.cpp b/third_party/WebKit/Source/platform/heap/Heap.cpp
index ef9249c..665b546 100644
--- a/third_party/WebKit/Source/platform/heap/Heap.cpp
+++ b/third_party/WebKit/Source/platform/heap/Heap.cpp
@@ -2400,6 +2400,11 @@
 
 void Heap::reportMemoryUsageForTracing()
 {
+    bool gcTracingEnabled;
+    TRACE_EVENT_CATEGORY_GROUP_ENABLED("blink_gc", &gcTracingEnabled);
+    if (!gcTracingEnabled)
+        return;
+
     // These values are divided by 1024 to avoid overflow in practical cases (TRACE_COUNTER values are 32-bit ints).
     // They are capped to INT_MAX just in case.
     TRACE_COUNTER1("blink_gc", "Heap::allocatedObjectSizeKB", std::min(Heap::allocatedObjectSize() / 1024, static_cast<size_t>(INT_MAX)));