Add on-by-default tracing to FrameView::invalidateTree which adds more debug info

Source/core/frame/FrameView.cpp

Index: Source/core/frame/FrameView.cpp
diff --git a/Source/core/frame/FrameView.cpp b/Source/core/frame/FrameView.cpp
index 93cad241d7a5581b884c9ca8479d5da7817ce7a3..28d38a514728b97e0cfd0ecc9331fc7ddd416d67 100644
--- a/Source/core/frame/FrameView.cpp
+++ b/Source/core/frame/FrameView.cpp
@@ -1042,8 +1042,12 @@ void FrameView::invalidateTree(RenderObject* root)
     // we continue to track paint invalidation rects until this function is called.
     ASSERT(!m_nestedLayoutCount);
 
-    TRACE_EVENT1(TRACE_DISABLED_BY_DEFAULT("blink.invalidation"), "FrameView::invalidateTree",
-        "root", TRACE_STR_COPY(root->debugName().ascii().data()));
+    const char* debugData = "unknown";
+    bool isTracing;
+    TRACE_EVENT_CATEGORY_GROUP_ENABLED(TRACE_DISABLED_BY_DEFAULT("blink.invalidation"), &isTracing);
+    if (isTracing)
+        debugData = root->debugName().ascii().data();

[esprehn, 2014/06/07 02:20:40]

All you're trying to do is save the one virtual call and the malloc for the
string here?

Also I don't think this is correct, the CString that created in ascii() will be
free by the time you get to the trace event below which should result in
crashes. You'd need to store the CString in a local.

+    TRACE_EVENT1("blink", "FrameView::invalidateTree", "root", TRACE_STR_COPY(debugData));
 
     // FIXME: really, we're in the paint invalidation phase here, and the compositing queries are legal.
     // Until those states are fully fledged, I'll just disable the ASSERTS.