Add slider minimum interaction time (#15358)

This change makes the discrete slider show the value indicator for a minimum amount of time for any interaction (tap, drag).

packages/flutter/lib/src/material/slider_theme.dart

@@ -469,19 +469,19 @@ class SliderThemeData extends Diagnosticable {
     );
     description.add(new DiagnosticsProperty<Color>('activeRailColor', activeRailColor, defaultValue: defaultData.activeRailColor));
     description.add(new DiagnosticsProperty<Color>('inactiveRailColor', inactiveRailColor, defaultValue: defaultData.inactiveRailColor));
-    description.add(new DiagnosticsProperty<Color>('disabledActiveRailColor', disabledActiveRailColor, defaultValue: defaultData.disabledActiveRailColor));
-    description.add(new DiagnosticsProperty<Color>('disabledInactiveRailColor', disabledInactiveRailColor, defaultValue: defaultData.disabledInactiveRailColor));
-    description.add(new DiagnosticsProperty<Color>('activeTickMarkColor', activeTickMarkColor, defaultValue: defaultData.activeTickMarkColor));
-    description.add(new DiagnosticsProperty<Color>('inactiveTickMarkColor', inactiveTickMarkColor, defaultValue: defaultData.inactiveTickMarkColor));
-    description.add(new DiagnosticsProperty<Color>('disabledActiveTickMarkColor', disabledActiveTickMarkColor, defaultValue: defaultData.disabledActiveTickMarkColor));
-    description.add(new DiagnosticsProperty<Color>('disabledInactiveTickMarkColor', disabledInactiveTickMarkColor, defaultValue: defaultData.disabledInactiveTickMarkColor));
+    description.add(new DiagnosticsProperty<Color>('disabledActiveRailColor', disabledActiveRailColor, defaultValue: defaultData.disabledActiveRailColor, level: DiagnosticLevel.debug));
+    description.add(new DiagnosticsProperty<Color>('disabledInactiveRailColor', disabledInactiveRailColor, defaultValue: defaultData.disabledInactiveRailColor, level: DiagnosticLevel.debug));
+    description.add(new DiagnosticsProperty<Color>('activeTickMarkColor', activeTickMarkColor, defaultValue: defaultData.activeTickMarkColor, level: DiagnosticLevel.debug));
+    description.add(new DiagnosticsProperty<Color>('inactiveTickMarkColor', inactiveTickMarkColor, defaultValue: defaultData.inactiveTickMarkColor, level: DiagnosticLevel.debug));
+    description.add(new DiagnosticsProperty<Color>('disabledActiveTickMarkColor', disabledActiveTickMarkColor, defaultValue: defaultData.disabledActiveTickMarkColor, level: DiagnosticLevel.debug));
+    description.add(new DiagnosticsProperty<Color>('disabledInactiveTickMarkColor', disabledInactiveTickMarkColor, defaultValue: defaultData.disabledInactiveTickMarkColor, level: DiagnosticLevel.debug));
     description.add(new DiagnosticsProperty<Color>('thumbColor', thumbColor, defaultValue: defaultData.thumbColor));
-    description.add(new DiagnosticsProperty<Color>('disabledThumbColor', disabledThumbColor, defaultValue: defaultData.disabledThumbColor));
-    description.add(new DiagnosticsProperty<Color>('overlayColor', overlayColor, defaultValue: defaultData.overlayColor));
+    description.add(new DiagnosticsProperty<Color>('disabledThumbColor', disabledThumbColor, defaultValue: defaultData.disabledThumbColor, level: DiagnosticLevel.debug));
+    description.add(new DiagnosticsProperty<Color>('overlayColor', overlayColor, defaultValue: defaultData.overlayColor, level: DiagnosticLevel.debug));
     description.add(new DiagnosticsProperty<Color>('valueIndicatorColor', valueIndicatorColor, defaultValue: defaultData.valueIndicatorColor));
-    description.add(new DiagnosticsProperty<SliderComponentShape>('thumbShape', thumbShape, defaultValue: defaultData.thumbShape));
-    description.add(new DiagnosticsProperty<SliderComponentShape>('valueIndicatorShape', valueIndicatorShape, defaultValue: defaultData.valueIndicatorShape));
-    description.add(new DiagnosticsProperty<ShowValueIndicator>('showValueIndicator', showValueIndicator, defaultValue: defaultData.showValueIndicator));
+    description.add(new DiagnosticsProperty<SliderComponentShape>('thumbShape', thumbShape, defaultValue: defaultData.thumbShape, level: DiagnosticLevel.debug));
+    description.add(new DiagnosticsProperty<SliderComponentShape>('valueIndicatorShape', valueIndicatorShape, defaultValue: defaultData.valueIndicatorShape, level: DiagnosticLevel.debug));
+    description.add(new EnumProperty<ShowValueIndicator>('showValueIndicator', showValueIndicator, defaultValue: defaultData.showValueIndicator));
   }
 }
 
@@ -595,8 +595,8 @@ class PaddleSliderValueIndicatorShape extends SliderComponentShape {
 
   // Radius of the top lobe of the value indicator.
   static const double _topLobeRadius = 16.0;
-  // Baseline size of the label text. This is the size that the value indicator
-  // was designed to contain. We scale if from here to fit other sizes.
+  // Designed size of the label text. This is the size that the value indicator
+  // was designed to contain. We scale it from here to fit other sizes.
   static const double _labelTextDesignSize = 14.0;
   // Radius of the bottom lobe of the value indicator.
   static const double _bottomLobeRadius = 6.0;