Warn about extractTypeNameFromFunctionName usage

BUG=519650

Review URL: https://codereview.chromium.org/1307743008

git-svn-id: svn://svn.chromium.org/blink/trunk@201520 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/wtf/InstanceCounter.h

@@ -34,6 +34,10 @@ namespace WTF {
 class String;
 WTF_EXPORT String dumpRefCountedInstanceCounts();
 
+// Warning: Using extractTypeNameFromFunctionName bloats binary size.
+// This function should be only used for debug and profiling purposes,
+// and should be never enabled on release builds.
+// TODO(kouhei): Move this inside #if when all dependencies are removed.
 WTF_EXPORT String extractTypeNameFromFunctionName(const char* funcName);
 
 template<typename T>