Allow updating scale defaults

docs/01-Scales.md

@@ -299,3 +299,15 @@ The radial linear scale extends the core scale class with the following tick tem
 	},
 }
 ```
+
+### Update Default Scale config
+The default configuration for a scale can be easily changed using the scale service. Pass in a partial configuration that will be merged with the current scale default configuration.
+
+For example, to set the minimum value of 0 for all linear scales, you would do the following. Any linear scales created after this time would now have a minimum of 0.
+```
+Chart.scaleService.updateScaleDefaults('linear', {
+	ticks: {
+		min: 0
+	}
+})
+```

src/core/core.scaleService.js

@@ -24,6 +24,12 @@ module.exports = function(Chart) {
 			// Return the scale defaults merged with the global settings so that we always use the latest ones
 			return this.defaults.hasOwnProperty(type) ? helpers.scaleMerge(Chart.defaults.scale, this.defaults[type]) : {};
 		},
+		updateScaleDefaults: function(type, additions) {
+			var defaults = this.defaults;
+			if (defaults.hasOwnProperty(type)) {
+				defaults[type] = helpers.extend(defaults[type], additions);
+			}
+		},
 		addScalesToLayout: function(chartInstance) {
 			// Adds each scale to the chart.boxes array to be sized accordingly
 			helpers.each(chartInstance.scales, function(scale) {

test/core.scaleService.tests.js

@@ -0,0 +1,29 @@
+// Tests of the scale service
+describe('Test the scale service', function() {
+
+	it('should update scale defaults', function() {
+		var defaults = {
+			testProp: true
+		};
+		var type = 'my_test_type';
+		var Constructor = function() {
+			this.initialized = true;
+		};
+		Chart.scaleService.registerScaleType(type, Constructor, defaults);
+
+		// Should equal defaults but not be an identical object
+		expect(Chart.scaleService.getScaleDefaults(type)).toEqual(jasmine.objectContaining({
+			testProp: true
+		}));
+		
+		Chart.scaleService.updateScaleDefaults(type, {
+			testProp: 'red',
+			newProp: 42
+		});
+
+		expect(Chart.scaleService.getScaleDefaults(type)).toEqual(jasmine.objectContaining({
+			testProp: 'red',
+			newProp: 42
+		}));
+	});
+});