[Impeller] fix Xcode frame capture.

impeller/renderer/backend/metal/surface_mtl.mm

@@ -153,6 +153,20 @@
   return IRect::MakeSize(resolve_texture_->GetSize());
 }
 
+static bool ShouldWaitForCommandBuffer() {
+#if ((FML_OS_MACOSX && !FML_OS_IOS) || FML_OS_IOS_SIMULATOR)
+  // If a transaction is present, `presentDrawable` will present too early. And
+  // so we wait on an empty command buffer to get scheduled instead, which
+  // forces us to also wait for all of the previous command buffers in the queue
+  // to get scheduled.
+  return true;
+#else
+  // On Physical iOS devices we still need to wait if we're taking a frame
+  // capture.
+  return [[MTLCaptureManager sharedCaptureManager] isCapturing];
+#endif  // ((FML_OS_MACOSX && !FML_OS_IOS) || FML_OS_IOS_SIMULATOR)
+}
+
 // |Surface|
 bool SurfaceMTL::Present() const {
   if (drawable_ == nil) {
@@ -179,17 +193,12 @@
     }
   }
 
-#if ((FML_OS_MACOSX && !FML_OS_IOS) || FML_OS_IOS_SIMULATOR)
-  // If a transaction is present, `presentDrawable` will present too early. And
-  // so we wait on an empty command buffer to get scheduled instead, which
-  // forces us to also wait for all of the previous command buffers in the queue
-  // to get scheduled.
-  id<MTLCommandBuffer> command_buffer =
-      ContextMTL::Cast(context.get())->CreateMTLCommandBuffer();
-  [command_buffer commit];
-  [command_buffer waitUntilScheduled];
-#endif  // ((FML_OS_MACOSX && !FML_OS_IOS) || FML_OS_IOS_SIMULATOR)
-
+  if (ShouldWaitForCommandBuffer()) {
+    id<MTLCommandBuffer> command_buffer =
+        ContextMTL::Cast(context.get())->CreateMTLCommandBuffer();
+    [command_buffer commit];
+    [command_buffer waitUntilScheduled];
+  }
   [drawable_ present];
 
   return true;