Unify SystraceSection.h implementation (facebook#35353)

Summary:
Pull Request resolved: facebook#35353

Unfortunately we have 2 different definitions of SystraceSection.h
- xplat/js/react-native-github/ReactCommon/cxxreact/SystraceSection.h
- xplat/js/react-native-github/ReactCommon/react/renderer/debug/SystraceSection.h

The first one is the Old Arch one and the second one is the New Arch one.

As we first step, we unify the implementation

Changelog: [Internal]

Reviewed By: rshest

Differential Revision: D41307049

fbshipit-source-id: a9eb854dfcf49f87ad81fd9cc8dbe51648ecd209

ReactCommon/react/renderer/debug/SystraceSection.h

@@ -14,6 +14,16 @@
 namespace facebook {
 namespace react {
 
+/**
+ * Allow providing an fbsystrace implementation that can short-circuit out
+ * quickly and can throttle too frequent events so we can get useful traces even
+ * if rendering etc. is spinning. For throttling we'll need file/line info so we
+ * use a macro.
+ */
+#if defined(WITH_LOOM_TRACE)
+#define SystraceSection                                         \
+  static constexpr const char systraceSectionFile[] = __FILE__; \
+  fbsystrace::FbSystraceSection<systraceSectionFile, __LINE__>
 /**
  * This is a convenience class to avoid lots of verbose profiling
  * #ifdefs.  If WITH_FBSYSTRACE is not defined, the optimizer will
@@ -23,7 +33,7 @@ namespace react {
  * different values in different files, there is no inconsistency in the sizes
  * of defined symbols.
  */
-#ifdef WITH_FBSYSTRACE
+#elif defined(WITH_FBSYSTRACE)
 struct ConcreteSystraceSection {
  public:
   template <typename... ConvertsToStringPiece>
@@ -41,8 +51,8 @@ struct DummySystraceSection {
  public:
   template <typename... ConvertsToStringPiece>
   explicit DummySystraceSection(
-      const char *name,
-      ConvertsToStringPiece &&...args) {}
+      __unused const char *name,
+      __unused ConvertsToStringPiece &&...args) {}
 };
 using SystraceSection = DummySystraceSection;
 #endif