Bug 1694721 - Don't do a debug render if there is no debug overlay. r=gw

When toggling debug state, we can sometimes queue debug renders, without
any debug overlay to send them to. This patch ensures we don't actually
draw anything in the debug renderer when there is no debug overlay.

Differential Revision: https://phabricator.services.mozilla.com/D111355

gfx/wr/webrender/src/renderer/mod.rs

@@ -2185,16 +2185,17 @@ impl Renderer {
         let _gm = self.gpu_profiler.start_marker("end frame");
         self.gpu_profiler.end_frame();
 
-        if let Some(device_size) = device_size {
+        let debug_overlay = device_size.and_then(|device_size| {
             // Bind a surface to draw the debug / profiler information to.
-            if let Some(draw_target) = self.bind_debug_overlay(device_size) {
+            self.bind_debug_overlay(device_size).map(|draw_target| {
                 self.draw_render_target_debug(&draw_target);
                 self.draw_texture_cache_debug(&draw_target);
                 self.draw_gpu_cache_debug(device_size);
                 self.draw_zoom_debug(device_size);
                 self.draw_epoch_debug();
-            }
-        }
+                draw_target
+            })
+        });
 
         self.profile.end_time(profiler::RENDERER_TIME);
         self.profile.end_time_if_started(profiler::TOTAL_FRAME_CPU_TIME);
@@ -2270,9 +2271,11 @@ impl Renderer {
                 CompositorKind::Native { .. } => true,
                 CompositorKind::Draw { .. } => self.device.surface_origin_is_top_left(),
             };
+            // If there is a debug overlay, render it. Otherwise, just clear
+            // the debug renderer.
             debug_renderer.render(
                 &mut self.device,
-                device_size,
+                debug_overlay.and(device_size),
                 scale,
                 surface_origin_is_top_left,
             );
@@ -2282,7 +2285,7 @@ impl Renderer {
         self.texture_upload_pbo_pool.end_frame(&mut self.device);
         self.device.end_frame();
 
-        if device_size.is_some() {
+        if debug_overlay.is_some() {
             self.last_time = current_time;
 
             // Unbind the target for the debug overlay. No debug or profiler drawing