[ios] Set contentsScale before we commit CATransaction (flutter#8218)

Layout occurs after [CATransaction commit]. layoutSubviews was where we set the contentsScale on the CALayer. This meant that for one frame, we would see content on the overlay view which was did not have the correct content scale.

This change makes it so that we initialize the FlutterOverlayView with the correct contentsScale.

This also updates the overlay_gr_context_ when we first create the overlay_view. This is an artifact of flutter#8175.

This manifests as jank as seen in: flutter/flutter#29573

Author: iskakaushik

shell/platform/darwin/ios/framework/Source/FlutterOverlayView.h

@@ -23,6 +23,7 @@
 - (instancetype)initWithCoder:(NSCoder*)aDecoder NS_UNAVAILABLE;
 
 - (instancetype)init NS_DESIGNATED_INITIALIZER;
+- (instancetype)initWithContentsScale:(CGFloat)contentsScale;
 - (std::unique_ptr<shell::IOSSurface>)createSoftwareSurface;
 - (std::unique_ptr<shell::IOSSurfaceGL>)createGLSurfaceWithContext:
     (std::shared_ptr<shell::IOSGLContext>)gl_context;

shell/platform/darwin/ios/framework/Source/FlutterOverlayView.mm

@@ -21,13 +21,13 @@
 @implementation FlutterOverlayView
 
 - (instancetype)initWithFrame:(CGRect)frame {
-  @throw([NSException exceptionWithName:@"FlutterOverlayView must initWithDelegate"
+  @throw([NSException exceptionWithName:@"FlutterOverlayView must init or initWithContentsScale"
                                  reason:nil
                                userInfo:nil]);
 }
 
 - (instancetype)initWithCoder:(NSCoder*)aDecoder {
-  @throw([NSException exceptionWithName:@"FlutterOverlayView must initWithDelegate"
+  @throw([NSException exceptionWithName:@"FlutterOverlayView must init or initWithContentsScale"
                                  reason:nil
                                userInfo:nil]);
 }
@@ -43,16 +43,17 @@ - (instancetype)init {
   return self;
 }
 
-- (void)layoutSubviews {
+- (instancetype)initWithContentsScale:(CGFloat)contentsScale {
+  self = [self init];
+
   if ([self.layer isKindOfClass:[CAEAGLLayer class]]) {
     CAEAGLLayer* layer = reinterpret_cast<CAEAGLLayer*>(self.layer);
     layer.allowsGroupOpacity = NO;
-    CGFloat screenScale = [UIScreen mainScreen].scale;
-    layer.contentsScale = screenScale;
-    layer.rasterizationScale = screenScale;
+    layer.contentsScale = contentsScale;
+    layer.rasterizationScale = contentsScale;
   }
 
-  [super layoutSubviews];
+  return self;
 }
 
 + (Class)layerClass {

shell/platform/darwin/ios/framework/Source/FlutterPlatformViews.mm

@@ -245,7 +245,6 @@
 
     active_composition_order_.push_back(view_id);
   }
-
   composition_order_.clear();
   return did_submit;
 }
@@ -294,7 +293,9 @@
     }
     return;
   }
-  FlutterOverlayView* overlay_view = [[FlutterOverlayView alloc] init];
+  auto contentsScale = flutter_view_.get().layer.contentsScale;
+  FlutterOverlayView* overlay_view =
+      [[FlutterOverlayView alloc] initWithContentsScale:contentsScale];
   overlay_view.frame = flutter_view_.get().bounds;
   overlay_view.autoresizingMask =
       (UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight);
@@ -303,6 +304,7 @@
   std::unique_ptr<Surface> surface = ios_surface->CreateSecondaryGPUSurface(gr_context);
   overlays_[overlay_id] = std::make_unique<FlutterPlatformViewLayer>(
       fml::scoped_nsobject<UIView>(overlay_view), std::move(ios_surface), std::move(surface));
+  overlays_gr_context_ = gr_context;
 }
 
 }  // namespace shell