Implement resize detection with DOM polling

lib/minimap-element.coffee

@@ -1,3 +1,4 @@
+{debounce} = require 'underscore-plus'
 {CompositeDisposable} = require 'event-kit'
 DOMStylesReader = require './mixins/dom-styles-reader'
 CanvasDrawer = require './mixins/canvas-drawer'
@@ -6,6 +7,10 @@ class MinimapElement extends HTMLElement
   DOMStylesReader.includeInto(this)
   CanvasDrawer.includeInto(this)
 
+  domPollingInterval: 100
+  domPollingIntervalId: null
+  domPollingPaused: false
+
   createdCallback: ->
     @subscriptions = new CompositeDisposable
     @initializeContent()
@@ -14,6 +19,7 @@ class MinimapElement extends HTMLElement
     @getTextEditorElementRoot().appendChild(this)
 
   attachedCallback: ->
+    @domPollingIntervalId = setInterval((=> @pollDOM()), @domPollingInterval)
     @measureHeightAndWidth()
     @requestUpdate()
 
@@ -40,6 +46,23 @@ class MinimapElement extends HTMLElement
     @visibleArea.classList.add('minimap-visible-area')
     @shadowRoot.appendChild(@visibleArea)
 
+  pauseDOMPolling: ->
+    @domPollingPaused = true
+    @resumeDOMPollingAfterDelay ?= debounce(@resumeDOMPolling, 100)
+    @resumeDOMPollingAfterDelay()
+
+  resumeDOMPolling: ->
+    @domPollingPaused = false
+
+  resumeDOMPollingAfterDelay: null
+
+  pollDOM: ->
+    return if @domPollingPaused or @updateRequested
+
+    if @width isnt @clientWidth or @height isnt @clientHeight
+      @measureHeightAndWidth()
+      @requestUpdate()
+
   measureHeightAndWidth: ->
     @width = @clientWidth
     @height = @clientHeight

spec/minimap-element-spec.coffee

@@ -128,3 +128,22 @@ describe 'MinimapElement', ->
         it 'updates the visible area', ->
           expect(visibleArea.offsetTop).toBeCloseTo(minimap.getTextEditorScrollTop() - minimap.getMinimapScrollTop(), 0)
           expect(visibleArea.offsetLeft).toBeCloseTo(minimap.getTextEditorScrollLeft(), 0)
+
+      describe 'when the editor is resized to a greater size', ->
+        beforeEach ->
+          height = editor.getHeight()
+          editorElement.style.width = '300px'
+          editorElement.style.height = '300px'
+
+          waitsFor -> editor.getHeight() isnt height
+
+          runs ->
+            advanceClock(150)
+            nextAnimationFrame()
+
+        it 'detect the resize and adjust itself', ->
+          expect(minimapElement.offsetWidth).toBeCloseTo(editorElement.offsetWidth / 11, 0)
+          expect(minimapElement.offsetHeight).toEqual(editorElement.offsetHeight)
+
+          expect(canvas.offsetWidth).toEqual(minimapElement.offsetWidth)
+          expect(canvas.offsetHeight).toEqual(minimapElement.offsetHeight + minimap.getLineHeight())