Add a way to pass in a preconstructed value to ManagedStatic (#2175)

A lot of our cases don't need the lazy construction, but do need manual destruction.

wpiutil/src/test/native/ManagedStaticTest.cpp

@@ -0,0 +1,60 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2019 FIRST. All Rights Reserved.                             */
+/* Open Source Software - may be modified and shared by FRC teams. The code   */
+/* must be accompanied by the FIRST BSD license file in the root directory of */
+/* the project.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#include "wpi/ManagedStatic.h"  // NOLINT(build/include_order)
+
+#include "gtest/gtest.h"
+
+static int refCount = 0;
+
+struct StaticTestClass {
+  StaticTestClass() { refCount++; }
+  ~StaticTestClass() { refCount--; }
+
+  void Func() {}
+};
+
+namespace wpi {
+TEST(ManagedStaticTest, LazyDoesNotInitialize) {
+  {
+    refCount = 0;
+    wpi::ManagedStatic<StaticTestClass> managedStatic;
+    ASSERT_EQ(refCount, 0);
+  }
+  ASSERT_EQ(refCount, 0);
+  wpi_shutdown();
+}
+
+TEST(ManagedStaticTest, LazyInitDoesntDestruct) {
+  {
+    refCount = 0;
+    wpi::ManagedStatic<StaticTestClass> managedStatic;
+    ASSERT_EQ(refCount, 0);
+    managedStatic->Func();
+    ASSERT_EQ(refCount, 1);
+  }
+  ASSERT_EQ(refCount, 1);
+  wpi_shutdown();
+  ASSERT_EQ(refCount, 0);
+}
+
+TEST(ManagedStaticTest, EagerInit) {
+  {
+    refCount = 0;
+    StaticTestClass* test = new StaticTestClass{};
+    ASSERT_EQ(refCount, 1);
+    wpi::ManagedStatic<StaticTestClass> managedStatic(
+        test, [](void* val) { delete static_cast<StaticTestClass*>(val); });
+    ASSERT_EQ(refCount, 1);
+    managedStatic->Func();
+    ASSERT_EQ(refCount, 1);
+  }
+  ASSERT_EQ(refCount, 1);
+  wpi_shutdown();
+  ASSERT_EQ(refCount, 0);
+}
+}  // namespace wpi