Resolve at definition time if a browser built-in method or our polyfill should be used, so avoid checking it for each call. Also, `helpers.extend` doesn't need to iterate two times on the function arguments. Finally, remove helpers never referenced.
Usage: If a label is an `array` as opposed to a `string` i.e. `[["June","2015"], "July"]` then each element is treated as a seperate line. The appropriate calculations are made to determine the correct height and width, and rotation is still supported.
view samples/line-multiline-labels.html to see it working.
On branch multiline_labels
Changes to be committed:
modified: docs/03-Line-Chart.md
new file: samples/line-multiline-labels.html
modified: src/core/core.helpers.js
modified: src/core/core.scale.js
Old versions of FF doesn't accept accessing the computed style via the 'max-width' and 'max-height' CSS notations using brackets, in which case the returned value is undefined. Changed the constraint methods to use maxWidth and mawHeight instead and make sure to test valid values.
The Chart.helpers.each method uses Object.keys() to iterates on the object *own enumerable properties*, meaning that checking if object.hasOwnProperty() is useless.
The core.helpers file was failing linting checks as the global CanvasPattern was not defined. Added the `/* global CanvasGradient */` statement to make linting pass. Updates chartjs/Chart.js#1323
When a hover background isn't specified in the config for a chart a modified version of the default color is used. If the background color is a CanvasPattern object an error is triggered.
With this change the default background color will no longer be modified if it is a CanvasPattern.
Introduced a new meta.hidden 3 states flag (null|true|false) to be able to override dataset.hidden when interacting with the chart (i.e., true or false to ignore the dataset.hidden value). This is required in order to be able to correctly share dataset.hidden between multiple charts.
For example: 2 charts are sharing the same data and dataset.hidden is initially false: the dataset will be displayed on both charts because meta.hidden is null. If the user clicks the legend of the first chart, meta.hidden is changed to true and the dataset is only hidden on the first chart. If dataset.hidden changes, only the second chart will have the dataset visibility updated and that until the user click again on the first chart legend, switching the meta.hidden to null.
Meta info are now scoped by chart and moved under the dataset._meta map { chart.id -> meta }. Meta for a specific chart (and dataset) can be accessed using chart.getDatasetMeta(datasetIndex) or from the dataset controller using getMeta(). Note that helpers.uid() now generates an int (instead of a string) to make lookups in the _meta map faster.
