Use different symbols for SystraceSection depending on WITH_FBYSTRACE

Reviewed By: tmikov

Differential Revision: D6365162

fbshipit-source-id: d1e13b0012528305506c368d5e60f3754a576df3

Author: Peter Ammon

Diff for: ReactCommon/cxxreact/SystraceSection.h

@@ -13,21 +13,33 @@ namespace react {
  * This is a convenience class to avoid lots of verbose profiling
  * #ifdefs.  If WITH_FBSYSTRACE is not defined, the optimizer will
  * remove this completely.  If it is defined, it will behave as
- * FbSystraceSection, with the right tag provided.
+ * FbSystraceSection, with the right tag provided. Use two separate classes to
+ * to ensure that the ODR rule isn't violated, that is, if WITH_FBSYSTRACE has
+ * different values in different files, there is no inconsistency in the sizes
+ * of defined symbols.
  */
-struct SystraceSection {
+#ifdef WITH_FBSYSTRACE
+struct ConcreteSystraceSection {
 public:
   template<typename... ConvertsToStringPiece>
-  explicit SystraceSection(const char* name, ConvertsToStringPiece&&... args)
-#ifdef WITH_FBSYSTRACE
+  explicit
+  ConcreteSystraceSection(const char* name, ConvertsToStringPiece&&... args)
     : m_section(TRACE_TAG_REACT_CXX_BRIDGE, name, args...)
-#endif
   {}
 
 private:
-#ifdef WITH_FBSYSTRACE
   fbsystrace::FbSystraceSection m_section;
-#endif
 };
+using SystraceSection = ConcreteSystraceSection;
+#else
+struct DummySystraceSection {
+public:
+  template<typename... ConvertsToStringPiece>
+  explicit
+  DummySystraceSection(const char* name, ConvertsToStringPiece&&... args)
+    {}
+};
+using SystraceSection = DummySystraceSection;
+#endif
 
 }}