UMG/Slate - Exposing the Widget Caching flag to the widget reflector. Also making it so invalidation is disabled when Picking Widgets is occuring, as invalidation causes that system of traversing the widget hierarchy to no longer function. Since it pretends there are no children to avoid Slate doing more work than it needs to.

[CL 2695558 by Nick Darnell in Main branch]

Engine/Source/Developer/SlateReflector/Private/Widgets/SWidgetReflector.cpp

@@ -210,6 +210,11 @@ private:
 		{
 			bShowFocus = false;
 			SetUIMode(EWidgetReflectorUIMode::Live);
+			SInvalidationPanel::SetEnableWidgetCaching(false);
+		}
+		else
+		{
+			SInvalidationPanel::SetEnableWidgetCaching(true);
 		}
 
 		return FReply::Handled();
@@ -611,6 +616,31 @@ TSharedRef<SDockTab> SWidgetReflector::SpawnWidgetHierarchyTab(const FSpawnTabAr
 						SNew(STextBlock)
 						.Text(LOCTEXT("ShowFocus", "Show Focus"))
 					]
+
+					+ SHorizontalBox::Slot()
+					.AutoWidth()
+					.Padding(5.0f)
+					[
+						SNew(SCheckBox)
+						.Style(FCoreStyle::Get(), "ToggleButtonCheckbox")
+						.IsChecked_Lambda([&]()
+						{
+							return SInvalidationPanel::GetEnableWidgetCaching() ? ECheckBoxState::Checked : ECheckBoxState::Unchecked;
+						})
+						.OnCheckStateChanged_Lambda([&](const ECheckBoxState NewState)
+						{
+							SInvalidationPanel::SetEnableWidgetCaching(( NewState == ECheckBoxState::Checked ) ? true : false);
+						})
+						[
+							SNew(SBox)
+							.VAlign(VAlign_Center)
+							.HAlign(HAlign_Center)
+							[
+								SNew(STextBlock)
+								.Text(LOCTEXT("EnableWidgetCaching", "Widget Caching"))
+							]
+						]
+					]
 				]
 
 				+SHorizontalBox::Slot()