Factor out LinearGradient and RadialGradient (#12155)

packages/flutter/lib/painting.dart

@@ -27,6 +27,7 @@ export 'src/painting/decoration.dart';
 export 'src/painting/edge_insets.dart';
 export 'src/painting/flutter_logo.dart';
 export 'src/painting/fractional_offset.dart';
+export 'src/painting/gradient.dart';
 export 'src/painting/text_painter.dart';
 export 'src/painting/text_span.dart';
 export 'src/painting/text_style.dart';

packages/flutter/lib/src/painting/border.dart

@@ -8,11 +8,8 @@ import 'package:flutter/foundation.dart';
 
 import 'basic_types.dart';
 import 'border_radius.dart';
-import 'decoration.dart';
 import 'edge_insets.dart';
 
-export 'edge_insets.dart' show EdgeInsets;
-
 /// The shape to use when rendering a [Border] or [BoxDecoration].
 enum BoxShape {
   /// An axis-aligned, 2D rectangle. May have rounded corners (described by a

packages/flutter/lib/src/painting/decoration.dart

@@ -10,9 +10,6 @@ import 'edge_insets.dart';
 
 export 'package:flutter/services.dart' show ImageConfiguration;
 
-export 'basic_types.dart' show Offset, Size;
-export 'edge_insets.dart' show EdgeInsets;
-
 // This group of classes is intended for painting in cartesian coordinates.
 
 /// A description of a box decoration (a decoration applied to a [Rect]).

packages/flutter/lib/src/painting/flutter_logo.dart

@@ -12,6 +12,7 @@ import 'package:flutter/foundation.dart';
 import 'basic_types.dart';
 import 'box_fit.dart';
 import 'decoration.dart';
+import 'edge_insets.dart';
 import 'fractional_offset.dart';
 import 'text_painter.dart';
 import 'text_span.dart';