Allow to end markers early

Summary:
Adds the ability to `MarkerSection` to end the marker before it goes out of scope.

This unlocks two scenarios:
- reuse the data associated with a marker after ending it.
- end markers in the middle of a function without adding arbitrary blocks.

Reviewed By: SidharthGuglani

Differential Revision: D15837840

fbshipit-source-id: c0afaeeabd169c65189b5028be54ea7dac3e3b84

yoga/Yoga.cpp

@@ -4026,9 +4026,7 @@ void YGNodeCalculateLayoutWithContext(
 #ifdef YG_ENABLE_EVENTS
   Event::publish<Event::LayoutPassStart>(node, {layoutContext});
 #endif
-  // unique pointer to allow ending the marker early
-  std::unique_ptr<marker::MarkerSection<YGMarkerLayout>> marker{
-      new marker::MarkerSection<YGMarkerLayout>{node}};
+  marker::MarkerSection<YGMarkerLayout> marker{node};
 
   // Increment the generation count. This will force the recursive routine to
   // visit all dirty nodes at least once. Subsequent visits will be skipped if
@@ -4087,7 +4085,7 @@ void YGNodeCalculateLayoutWithContext(
           true,
           "initial",
           node->getConfig(),
-          marker->data,
+          marker.data,
           layoutContext)) {
     node->setPosition(
         node->getLayout().direction, ownerWidth, ownerHeight, ownerWidth);
@@ -4104,12 +4102,11 @@ void YGNodeCalculateLayoutWithContext(
 #endif
   }
 
-#ifdef YG_ENABLE_EVENTS
-  Event::publish<Event::LayoutPassEnd>(node, {layoutContext, &marker->data});
-#endif
+  marker.end();
 
-  // end marker here
-  marker = nullptr;
+#ifdef YG_ENABLE_EVENTS
+  Event::publish<Event::LayoutPassEnd>(node, {layoutContext, &marker.data});
+#endif
 
   // We want to get rid off `useLegacyStretchBehaviour` from YGConfig. But we
   // aren't sure whether client's of yoga have gotten rid off this flag or not.

yoga/instrumentation.h

@@ -19,11 +19,13 @@ private:
 
 public:
   MarkerSection(YGNodeRef node) : MarkerSection{node, node->getConfig()} {}
-  ~MarkerSection() {
+  void end() {
     if (endMarker_) {
       endMarker_(MarkerType, node_, markerData(&data), userData_);
+      endMarker_ = nullptr;
     }
   }
+  ~MarkerSection() { end(); }
 
   typename Data::type data = {};