A low scope error message height fix for #3091 (#7685)

* Print the error message multiple times to avoid overlap with status bar and add paragraph to mock_canvas

packages/flutter/lib/src/rendering/error.dart

@@ -9,6 +9,8 @@ import 'object.dart';
 
 const double _kMaxWidth = 100000.0;
 const double _kMaxHeight = 100000.0;
+// Line length to fit small phones without dynamically checking size.
+const String line = '\n────────────────────\n\n';
 
 /// A render object used as a placeholder when an error occurs.
 ///
@@ -42,7 +44,10 @@ class RenderErrorBox extends RenderBox {
         // see the paragraph.dart file and the RenderParagraph class.
         ui.ParagraphBuilder builder = new ui.ParagraphBuilder(paragraphStyle);
         builder.pushStyle(textStyle);
-        builder.addText(message);
+        builder.addText(
+          '$message$line$message$line$message$line$message$line$message$line$message$line'
+          '$message$line$message$line$message$line$message$line$message$line$message'
+        );
         _paragraph = builder.build();
       }
     } catch (e) { }
@@ -79,14 +84,15 @@ class RenderErrorBox extends RenderBox {
 
   /// The text style to use when painting [RenderErrorBox] objects.
   static ui.TextStyle textStyle = new ui.TextStyle(
-    color: const Color(0xFFFFFF00),
+    color: const Color(0xFFFFFF66),
     fontFamily: 'monospace',
-    fontSize: 7.0
+    fontSize: 14.0,
+    fontWeight: FontWeight.bold
   );
 
   /// The paragraph style to use when painting [RenderErrorBox] objects.
   static ui.ParagraphStyle paragraphStyle = new ui.ParagraphStyle(
-    lineHeight: 0.25 // TODO(ianh): https://github.com/flutter/flutter/issues/2460 will affect this
+    lineHeight: 0.85
   );
 
   @override
@@ -104,6 +110,7 @@ class RenderErrorBox extends RenderBox {
           width = size.width;
         }
         _paragraph.layout(new ui.ParagraphConstraints(width: width));
+
         context.canvas.drawParagraph(_paragraph, offset);
       }
     } catch (e) { }

packages/flutter/test/rendering/error_test.dart

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:flutter_test/flutter_test.dart';
+import 'package:flutter/rendering.dart';
+import 'package:flutter/widgets.dart';
+
+import '../rendering/mock_canvas.dart';
+
+/// Unit tests error.dart's usage via ErrorWidget.
+void main() {
+  final String errorMessage = 'Some error message';
+
+  testWidgets('test draw error paragraph', (WidgetTester tester) async {
+    await tester.pumpWidget(new ErrorWidget(new Exception(errorMessage)));
+
+    expect(find.byType(ErrorWidget), paints
+        ..rect(rect: new Rect.fromLTWH(0.0, 0.0, 800.0, 600.0))
+        ..paragraph(offset: Offset.zero));
+  });
+}

packages/flutter/test/rendering/mock_canvas.dart

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:ui' as ui show Paragraph;
+
 import 'package:flutter/foundation.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter_test/flutter_test.dart';
@@ -182,6 +184,15 @@ abstract class PaintPattern {
   /// [Canvas.drawLine] call are ignored.
   void line({ Color color, bool hasMaskFilter, PaintingStyle style });
 
+  /// Indicates that a paragraph is expected next.
+  ///
+  /// Calls are skipped until a call to [Canvas.drawParagraph] is found. Any
+  /// arguments that are passed to this method are compared to the actual
+  /// [Canvas.drawParagraph] call's argument, and any mismatches result in failure.
+  ///
+  /// If no call to [Canvas.drawParagraph] was made, then this results in failure.
+  void paragraph({ ui.Paragraph paragraph, Offset offset });
+
   /// Provides a custom matcher.
   ///
   /// Each method call after the last matched call (if any) will be passed to
@@ -269,6 +280,11 @@ class _TestRecordingCanvasPatternMatcher extends Matcher implements PaintPattern
     _predicates.add(new _LinePaintPredicate(color: color, hasMaskFilter: hasMaskFilter, style: style));
   }
 
+  @override
+  void paragraph({ ui.Paragraph paragraph, Offset offset }) {
+    _predicates.add(new _FunctionPaintPredicate(#drawParagraph, <dynamic>[paragraph, offset]));
+  }
+
   @override
   void something(PaintPatternPredicate predicate) {
     _predicates.add(new _SomethingPaintPredicate(predicate));