fix(NUX): set smaller default window size for users with large monitors

Summary:
fixes T4080

set the maximum default viewport size to 1440x900, the screen resolution for a 15 inch macbook pro.

if the monitor is either wider or taller than the default, then cap the dimension and center it.

Test Plan: added tests

Reviewers: evan, bengotow

Reviewed By: evan, bengotow

Maniphest Tasks: T4080

Differential Revision: https://phab.nylas.com/D2115

spec/atom-spec.coffee

@@ -43,6 +43,34 @@ describe "the `atom` global", ->
         [actualWidth, h] = win.getMinimumSize()
         expect(actualWidth).toBe inputMinWidth
 
+    describe '::getDefaultWindowDimensions', ->
+      screen = require('remote').require 'screen'
+
+      it "returns primary display's work area size if it's small enough", ->
+        spyOn(screen, 'getPrimaryDisplay').andReturn workAreaSize: width: 1440, height: 900
+
+        out = atom.getDefaultWindowDimensions()
+        expect(out).toEqual x: 0, y: 0, width: 1440, height: 900
+
+      it "caps width at 1440 and centers it, if wider", ->
+        spyOn(screen, 'getPrimaryDisplay').andReturn workAreaSize: width: 1840, height: 900
+
+        out = atom.getDefaultWindowDimensions()
+        expect(out).toEqual x: 200, y: 0, width: 1440, height: 900
+
+      it "caps height at 900 and centers it, if taller", ->
+        spyOn(screen, 'getPrimaryDisplay').andReturn workAreaSize: width: 1440, height: 1100
+
+        out = atom.getDefaultWindowDimensions()
+        expect(out).toEqual x: 0, y: 100, width: 1440, height: 900
+
+      it "returns only the max viewport size if it's smaller than the defaults", ->
+        spyOn(screen, 'getPrimaryDisplay').andReturn workAreaSize: width: 1000, height: 800
+
+        out = atom.getDefaultWindowDimensions()
+        expect(out).toEqual x: 0, y: 0, width: 1000, height: 800
+
+
   describe ".isReleasedVersion()", ->
     it "returns false if the version is a SHA and true otherwise", ->
       version = '0.1.0'

src/atom.coffee

@@ -586,7 +586,20 @@ class Atom extends Model
   getDefaultWindowDimensions: ->
     screen = remote.require('screen')
     {width, height} = screen.getPrimaryDisplay().workAreaSize
-    {x: 0, y: 0, width, height}
+    x = 0
+    y = 0
+
+    MAX_WIDTH = 1440
+    if width > MAX_WIDTH
+      x = (width - MAX_WIDTH) / 2
+      width = MAX_WIDTH
+
+    MAX_HEIGHT = 900
+    if height > MAX_HEIGHT
+      y = (height - MAX_HEIGHT) / 2
+      height = MAX_HEIGHT
+
+    {x, y, width, height}
 
   restoreWindowDimensions: ->
     dimensions = @savedState.windowDimensions