Adds an `emplace()` method to RunOnExit, and deletes the move and copy constructors.

There's some evidence in CL 411404964 that the copy constructor is accidentally used in the ChromeOS Chromium build.

PiperOrigin-RevId: 411618225

http2/adapter/oghttp2_adapter_test.cc

diff --git a/http2/adapter/oghttp2_adapter_test.cc b/http2/adapter/oghttp2_adapter_test.cc
index 7d0ca8a..c3f4356 100644
--- a/http2/adapter/oghttp2_adapter_test.cc
+++ b/http2/adapter/oghttp2_adapter_test.cc
@@ -1836,7 +1836,7 @@
 }
 
 TEST(OgHttp2AdapterServerTest,
-     DISABLED_IncompleteRequestWithServerResponseRstStreamEnabled) {
+     IncompleteRequestWithServerResponseRstStreamEnabled) {
   DataSavingVisitor visitor;
   OgHttp2Adapter::Options options{.perspective = Perspective::kServer,
                                   .rst_stream_no_error_when_incomplete = true};

http2/adapter/oghttp2_session.cc

diff --git a/http2/adapter/oghttp2_session.cc b/http2/adapter/oghttp2_session.cc
index 168a9a0..0792a5c 100644
--- a/http2/adapter/oghttp2_session.cc
+++ b/http2/adapter/oghttp2_session.cc
@@ -127,8 +127,10 @@
   RunOnExit() = default;
   explicit RunOnExit(std::function<void()> f) : f_(std::move(f)) {}
 
-  RunOnExit(RunOnExit&& other) = default;
-  RunOnExit& operator=(RunOnExit&& other) = default;
+  RunOnExit(const RunOnExit& other) = delete;
+  RunOnExit& operator=(const RunOnExit& other) = delete;
+  RunOnExit(RunOnExit&& other) = delete;
+  RunOnExit& operator=(RunOnExit&& other) = delete;
 
   ~RunOnExit() {
     if (f_) {
@@ -137,6 +139,8 @@
     f_ = {};
   }
 
+  void emplace(std::function<void()> f) { f_ = std::move(f); }
+
  private:
   std::function<void()> f_;
 };
@@ -417,7 +421,7 @@
       streams_reset_.insert(frame->stream_id());
     } else if (iter != stream_map_.end()) {
       // Enqueue RST_STREAM NO_ERROR if appropriate.
-      r = RunOnExit{[this, iter]() { MaybeFinWithRstStream(iter); }};
+      r.emplace([this, iter]() { MaybeFinWithRstStream(iter); });
     }
   }
   if (frame->stream_id() != 0) {