Add focusPreviousPane to pane container

spec/app/pane-container-spec.coffee

@@ -39,6 +39,18 @@ describe "PaneContainer", ->
       container.focusNextPane()
       expect(pane1.activeItem).toMatchSelector ':focus'
 
+  describe ".focusPreviousPane()", ->
+    it "focuses the pane preceding the focused pane or the last pane if no pane has focus", ->
+      container.attachToDom()
+      container.focusPreviousPane()
+      expect(pane3.activeItem).toMatchSelector ':focus'
+      container.focusPreviousPane()
+      expect(pane2.activeItem).toMatchSelector ':focus'
+      container.focusPreviousPane()
+      expect(pane1.activeItem).toMatchSelector ':focus'
+      container.focusPreviousPane()
+      expect(pane3.activeItem).toMatchSelector ':focus'
+
   describe ".getActivePane()", ->
     it "returns the most-recently focused pane", ->
       focusStealer = $$ -> @div tabindex: -1, "focus stealer"

src/app/pane-container.coffee

@@ -32,6 +32,17 @@ class PaneContainer extends View
     else
       false
 
+  focusPreviousPane: ->
+    panes = @getPanes()
+    if panes.length > 1
+      currentIndex = panes.indexOf(@getFocusedPane())
+      previousIndex = currentIndex - 1
+      previousIndex = panes.length - 1 if previousIndex < 0
+      panes[previousIndex].focus()
+      true
+    else
+      false
+
   makeNextPaneActive: ->
     panes = @getPanes()
     currentIndex = panes.indexOf(@getActivePane())

src/app/root-view.coffee

@@ -53,6 +53,7 @@ class RootView extends View
       config.set("editor.fontSize", fontSize - 1) if fontSize > 1
 
     @command 'window:focus-next-pane', => @focusNextPane()
+    @command 'window:focus-previous-pane', => @focusPreviousPane()
     @command 'window:save-all', => @saveAll()
     @command 'window:toggle-invisibles', =>
       config.set("editor.showInvisibles", !config.get("editor.showInvisibles"))
@@ -143,6 +144,7 @@ class RootView extends View
   getActiveView: ->
     @panes.getActiveView()
 
+  focusPreviousPane: -> @panes.focusPreviousPane()
   focusNextPane: -> @panes.focusNextPane()
   getFocusedPane: -> @panes.getFocusedPane()