Fix Fiber::LocalData leak for large fiber locals

Summary: facepaw

Reviewed By: yfeldblum

Differential Revision: D4856227

fbshipit-source-id: 17a73d4d630c6efe1763bbd8aff8b7a2c7721c27

folly/fibers/Fiber.cpp

@@ -189,6 +189,10 @@ void Fiber::preempt(State state) {
   }
 }
 
+Fiber::LocalData::~LocalData() {
+  reset();
+}
+
 Fiber::LocalData::LocalData(const LocalData& other) : data_(nullptr) {
   *this = other;
 }

folly/fibers/Fiber.h

@@ -131,6 +131,7 @@ class Fiber {
   class LocalData {
    public:
     LocalData() {}
+    ~LocalData();
     LocalData(const LocalData& other);
     LocalData& operator=(const LocalData& other);