fix: repair three memory issues contributing to animated image leak (#429)

1. elinux_window.h: Fix display refresh rate reported to Flutter engine.
   frame_rate_ is in milliHz (e.g. 60000 for a 60 Hz display); dividing
   1000000 by it yielded ~16 instead of the required 60 Hz.
   FlutterEngineDisplay.refresh_rate expects frames-per-second. Correct
   formula is frame_rate_ / 1000.0.

2. elinux_window_wayland.cc: Add missing wl_callback_destroy() when
   wp_presentation is available and the done callback returns early.
   Without this the client-side wl_proxy object was leaked every time
   a new surface frame fires while wp_presentation is active.

3. elinux_egl_surface.cc: Guard PopulateExistingDamage against orphaned
   malloc. If the Flutter engine ever calls populate without a subsequent
   present_with_info (e.g. at shutdown or on a skipped frame), the
   previously allocated FlutterRect buffer is now freed before the new
   allocation rather than being silently overwritten.

Fixes: #429

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: aki1770-del

src/flutter/shell/platform/linux_embedded/surface/elinux_egl_surface.cc

@@ -166,6 +166,15 @@ void ELinuxEGLSurface::PopulateExistingDamage(const intptr_t fbo_id,
 
   existing_damage->num_rects = 1;
 
+  // Free any previous allocation for this FBO (defensive: guards against the
+  // engine calling populate without a subsequent present_with_info, which would
+  // otherwise orphan the malloc'd buffer).
+  auto it = existing_damage_map_.find(fbo_id);
+  if (it != existing_damage_map_.end() && it->second != nullptr) {
+    free(it->second);
+    it->second = nullptr;
+  }
+
   // Allocate the array of rectangles for the existing damage.
   existing_damage_map_[fbo_id] = static_cast<FlutterRect*>(
       malloc(sizeof(FlutterRect) * existing_damage->num_rects));

src/flutter/shell/platform/linux_embedded/window/elinux_window.h

@@ -45,7 +45,7 @@ class ELinuxWindow {
   void NotifyDisplayInfoUpdates() const {
     if (binding_handler_delegate_) {
       binding_handler_delegate_->UpdateDisplayInfo(
-          std::trunc(1000000.0 / frame_rate_), GetCurrentWidth(),
+          static_cast<double>(frame_rate_) / 1000.0, GetCurrentWidth(),
           GetCurrentHeight(), current_scale_);
     }
   }

src/flutter/shell/platform/linux_embedded/window/elinux_window_wayland.cc

@@ -269,6 +269,7 @@ const wl_callback_listener ELinuxWindowWayland::kWlSurfaceFrameListener = {
           // by all compositors. This path is for when it wasn't supported.
           auto self = reinterpret_cast<ELinuxWindowWayland*>(data);
           if (self->wp_presentation_clk_id_ != UINT32_MAX) {
+            wl_callback_destroy(wl_callback);
             return;
           }