Closes #114, #80; Removed isVisible.

Removed the method from the base class and all references from the source. Since we are no longer using the hack due to problems with the approach, we can close the performance test ticket (#80).

src/core/chart.coffee

@@ -65,13 +65,6 @@ class Epoch.Chart.Base extends Epoch.Events
       @width = defaults.width unless @width?
       @height = defaults.height unless @height?
 
-  # Determines if the chart is currently visible in a document.
-  # @return [Boolean] True if the chart is visible, false otherwise.
-  isVisible: ->
-    return true
-    #return false unless @el?
-    #@el.is('*:visible')
-
   # Set the initial data for the chart.
   # @param data Data to initially set for the given chart. The data format can vary
   #   from chart to chart. The base class assumes that the data provided will be an

src/time/area.coffee

@@ -69,7 +69,6 @@ class Epoch.Time.Area extends Epoch.Time.Stack
 
   # Draws the area chart.
   draw: (delta=0) ->
-    return unless @isVisible()
     @clear()
     @_drawAreas(delta)
     @_drawStrokes(delta)

src/time/bar.coffee

@@ -22,7 +22,6 @@ class Epoch.Time.Bar extends Epoch.Time.Stack
 
   # Draws the stacked bar chart.
   draw: (delta=0) ->
-    return unless @isVisible()
     @clear()
     [y, w] = [@y(), @w()]
 

src/time/gauge.coffee

@@ -103,8 +103,6 @@ class Epoch.Time.Gauge extends Epoch.Chart.Canvas
 
   # Draws the gauge.
   draw: ->
-    return unless @isVisible()
-
     [cx, cy, r] = [@centerX(), @centerY(), @radius()]
     [tickOffset, tickSize] = [@options.tickOffset, @options.tickSize]
 

src/time/heatmap.coffee

@@ -205,7 +205,6 @@ class Epoch.Time.Heatmap extends Epoch.Time.Plot
 
   # Copies the paint canvas onto the display canvas, thus rendering the heatmap.
   draw: (delta=0) ->
-    return unless @isVisible()
     @clear()
     @ctx.drawImage @paint, delta, 0
     super()