Base editor dimensions on the wrapper view

The goal is to make the editor behave like a standard block-level
element.

The horizontal behavior is simple: we stretch horizontally to fill our
container.

The vertical behavior is more nuanced. If an explicit height is assigned
on the wrapper view, we honor that height. But if no explicit height is
assigned, the editor stretches vertically so that its contents are
visible.

This prepares us to support mini editors, which need to be 1-line tall
without an explicit height assignment.

src/editor-component.coffee

@@ -759,21 +759,22 @@ EditorComponent = React.createClass
     return if @scrollViewMeasurementPaused
     return unless @isMounted()
 
-    {editor} = @props
-    editorNode = @getDOMNode()
+    {editor, parentView} = @props
+    parentNode = parentView.element
     scrollViewNode = @refs.scrollView.getDOMNode()
-    {position} = getComputedStyle(editorNode)
-    {width, height} = editorNode.style
+    {position} = getComputedStyle(parentNode)
+    {height} = parentNode.style
 
     if position is 'absolute' or height
       clientHeight =  scrollViewNode.clientHeight
       editor.setHeight(clientHeight) if clientHeight > 0
+    else
+      editor.setHeight(null)
 
-    if position is 'absolute' or width
-      clientWidth = scrollViewNode.clientWidth
-      paddingLeft = parseInt(getComputedStyle(scrollViewNode).paddingLeft)
-      clientWidth -= paddingLeft
-      editor.setWidth(clientWidth) if clientWidth > 0
+    clientWidth = scrollViewNode.clientWidth
+    paddingLeft = parseInt(getComputedStyle(scrollViewNode).paddingLeft)
+    clientWidth -= paddingLeft
+    editor.setWidth(clientWidth) if clientWidth > 0
 
   measureLineHeightAndCharWidthsIfNeeded: (prevState) ->
     if not isEqualForProperties(prevState, @state, 'lineHeight', 'fontSize', 'fontFamily')

static/editor.less

@@ -3,6 +3,10 @@
 @import "octicon-mixins";
 
 .editor.react {
+  .editor-contents {
+    width: 100%;
+  }
+
   .underlayer {
     position: absolute;
     top: 0;