[G3 Developer Discussion [Developers Only]] Kickoff:
I start this thread in order to share with you the information I already collected regarding the theming the navbar keys on stock roms. You should have realized that after Lollipop upgrade there is not even one stock based ROM or theme which contains themed navbar icons. The reason for this is:

1. Apktool RC3 is buggy on LG system apps, including LGSystemUI.apk. There is no way recently to decompile systemui and have access to the source code of the navbars.

2. With the Lollipop upgrade LG changed its approach regarding definition of the navbar icons using Google's new public classes of VectorDrawables.

java.lang.Object
↳android.graphics.drawable.Drawable
↳android.graphics.drawable.VectorDrawable

VectorDrawables are specific xml files that define vector graphics via vector coordinates.

The three main navbar icons are defined in LGSystemUI.apk as follows:

ic_sysbar_back_button.xml:

<?xml version="1.0" encoding="utf-8"?>
<vector android:height="42.0dip" android:width="42.0dip" android:viewportWidth="168.0" android:viewportHeight="168.0"
xmlns:android="http://schemas.android.com/apk/res/android">
<path android:fillColor="#ffffffff" android:pathData="M124.125,120.827h-76c-1.358,0-2.667-1.789-2.667-4c0-2.209,1.273-4,2.667-4h76c11.045,0,20-8.953,20-20 c0-11.046-8.955-19.999-20-19.999h-96v-8h96c15.463,0,28,12.535,28,27.999C152.125,108.292,139.588,120.827,124.125,120.827z" />
<path android:fillColor="#ffffffff" android:pathData="M45.447,54.302L30.36,66.189c0,0-1.581,1.291-0.553,2.639c-1.028,1.346,0.553,2.639,0.553,2.639 l15.086,11.886c0,0,3.054,2.04,0,5.447c-2.114,2.359-4.366,1.172-5.865,0L17.741,71.466c-1.291-1.074-1.616-2.639-1.616-2.639 s0.326-1.564,1.616-2.639l21.842-17.334c1.499-1.172,3.75-2.359,5.865,0C48.5,52.263,45.447,54.302,45.447,54.302z" />
</vector>

ic_sysbar_home_button.xml:

<?xml version="1.0" encoding="utf-8"?>
<vector android:height="48.0dip" android:width="48.0dip" android:viewportWidth="168.0" android:viewportHeight="168.0"
xmlns:android="http://schemas.android.com/apk/res/android">
<path android:fillColor="#ffffffff" android:pathData="M159.881,87.102l-0.541,1.217c-0.898,2.02-3.264,2.927-5.281,2.027L144.5,86.09c0,14.906,0,28.396,0,28.396 c0,2.209-1.791,4-4,4h-112c-2.209,0-4-1.791-4-4V86.09l-9.559,4.256c-2.018,0.898-4.382-0.009-5.281-2.027l-0.542-1.217 c-0.898-2.02,0.009-4.384,2.027-5.282l70.647-31.455c0.889-0.395,1.839-0.423,2.708-0.178c0.868-0.245,1.818-0.217,2.708,0.178 l70.647,31.455C159.873,82.718,160.781,85.082,159.881,87.102z M32.5,109.154c0,1.27,0.038,1.332,1.333,1.332h101.333 c1.244,0,1.334-0.047,1.334-1.332V82.528l-52-23.152l-52,23.152C32.5,95.766,32.5,109.154,32.5,109.154z" />
</vector>

ic_sysbar_recent_button.xml:

<?xml version="1.0" encoding="utf-8"?>
<vector android:height="42.0dip" android:width="42.0dip" android:viewportWidth="168.0" android:viewportHeight="168.0"
xmlns:android="http://schemas.android.com/apk/res/android">
<path android:fillColor="#ffffffff" android:pathData="M149,51.5H37c-2.209,0-5,1.027-5,3.236c0,0,0,5.764,0,10.764H21c-2.209,0-5,1.027-5,3.236v42.998 c0,2.211,2.791,4.766,5,4.766h112c2.209,0,3-2.555,3-4.766V101.5c8,0,13,0,13,0c2.209,0,3-2.555,3-4.766V54.736 C152,52.527,151.209,51.5,149,51.5z M128,106.402c0,1.285,0.91,2.098-0.333,2.098H26.333c-1.296,0-2.333-0.828-2.333-2.098V74.068 c0-1.27,1.038-0.568,2.333-0.568h101.333c1.243,0,0.333-0.716,0.333,0.568L128,106.402L128,106.402z M144,91.402 c0,1.285,0.91,2.098-0.333,2.098H136V68.736c0-2.209-0.791-3.236-3-3.236H40v-5.432c0-1.269,1.038-0.568,2.333-0.568h101.334 c1.243,0,0.333-0.716,0.333,0.568V91.402L144,91.402z" />
</vector>

I spent many dozen hours on finding/creating vector graphics of Lollipop navbar keys as SVG files. I tried many times and many ways to save the corresponding SVG files and convert them to VectorDrawable using this site: http://inloop.github.io/svg2android/

Used a trick to recompile the new xmls and replaced them in the LGSystemUI.apk with my vrtheme engine. But still no success. When the shape of the icon was OK the size of them was never.

Basically I am fully confused why the virtual canvas of the stock icons is 168x168. I am struggling with the fill and stroke color definition as well.

This is the status quo. I hope by starting this thread that together we can solve the problem and get the working source code of the Lollipop navbars. I look forward for any help.

Please note that skin1980 is already involved in the project and I got from him huge help with his intelligent hints.

This is a development thread please do not post comments and remarks that are not intended to provide professional help.

Merry Xmas to all of you!