chrome.app.runtime.onLaunched.addListener(function() {
	chrome.app.window.create('index.html', {
		'bounds': {
			'width': 1600,
			'height': 900
		}
	});
});
chrome.app.runtime.onLaunched.addListener(function() {
	chrome.app.window.create('index.html', {
		'bounds': {
			'width': 1280,
			'height': 800
		}
	});
});
--- 
+++ 
@@ -1,8 +1,8 @@
 chrome.app.runtime.onLaunched.addListener(function() {
 	chrome.app.window.create('index.html', {
 		'bounds': {
-			'width': 1600,
-			'height': 900
+			'width': 1280,
+			'height': 800
 		}
 	});
 });
Change default window resolution to 1600x900
