[flutter] Update fields for the prefer_final_fields Dart analyzer check

Change-Id: I10b8df87820630e722425fdf120c2b9137354868
diff --git a/session_shells/ermine/lib/src/widgets/status_graph_visualizer.dart b/session_shells/ermine/lib/src/widgets/status_graph_visualizer.dart
index 0acd112..f0f49b8 100644
--- a/session_shells/ermine/lib/src/widgets/status_graph_visualizer.dart
+++ b/session_shells/ermine/lib/src/widgets/status_graph_visualizer.dart
@@ -185,19 +185,19 @@
   // Data to be represented in graph.
   double _graphData;
   // Height of graph widget.
-  double _graphHeight;
+  final double _graphHeight;
   // Width of graph widget.
-  double _graphWidth;
+  final double _graphWidth;
   // Min data value found within data being plotted.
-  double _graphMin;
+  final double _graphMin;
   // Max data value found within data being plotted.
-  double _graphMax;
+  final double _graphMax;
   // Determines if graph visualization is first in order in row.
-  bool _graphFirst;
+  final bool _graphFirst;
   // If true, draws border around graph.
-  bool _borderActive;
+  final bool _borderActive;
   // Determines if graph is filled underneath.
-  bool _fillActive;
+  final bool _fillActive;
   final List<double> _graphDataList = List.filled(50, 0);
 
   StatusGraphVisualizerModel({
diff --git a/session_shells/ermine/lib/src/widgets/status_progress_bar_visualizer.dart b/session_shells/ermine/lib/src/widgets/status_progress_bar_visualizer.dart
index b234056..de94a78 100644
--- a/session_shells/ermine/lib/src/widgets/status_progress_bar_visualizer.dart
+++ b/session_shells/ermine/lib/src/widgets/status_progress_bar_visualizer.dart
@@ -127,13 +127,13 @@
   // Maximum amount the progress bar visualization can be filled.
   double _barMax;
   // Double between 0 - 1 that determines the ratio of bar to text in container.
-  double _barSize;
+  final double _barSize;
   // Height of bar visualization & text.
-  double _barHeight;
+  final double _barHeight;
   // Determines if bar visualization is first in order in row.
-  bool _barFirst;
+  final bool _barFirst;
   // Offsets bar from alignment axis.
-  double _offset;
+  final double _offset;
 
   set barValue(String updatedBarValue) {
     _barValue = updatedBarValue;
diff --git a/session_shells/ermine/lib/src/widgets/status_tick_bar_visualizer.dart b/session_shells/ermine/lib/src/widgets/status_tick_bar_visualizer.dart
index 0e55dfc..9071530 100644
--- a/session_shells/ermine/lib/src/widgets/status_tick_bar_visualizer.dart
+++ b/session_shells/ermine/lib/src/widgets/status_tick_bar_visualizer.dart
@@ -123,9 +123,9 @@
   // Maximum amount the bar visualization can be filled.
   double _barMax;
   // Maximum amount of tick marks allowed to be in row.
-  int _tickMax;
+  final int _tickMax;
   // Determines if bar visualization is first in order in row.
-  bool _barFirst;
+  final bool _barFirst;
 
   set barFill(double updatedBarFill) {
     _barFill = updatedBarFill;