What you're doing is correct, but seems like you're writing the switches to the wrong file for Chrome (and note that the file that you write the switches to may vary based on the OS version [or maybe phone?] ).

I tried this on two different phones, and had to write to two different files! Hopefully one of them will work for you:

Phone 1: Nexus 6 with Android 6.0.1

Simply do the following in adb shell:

echo "chrome --sync-url" > /data/local/tmp/chrome-command-line'

Phone 2: MotoG with Android 4.4.4

This is a bit trickier. It turned out that Chrome actually reads the switches from /data/local/chrome-command-line (not in the tmp subdirectory!). Now the issue is that on an unrooted phone you won't have permission to write to this file! So I had to root my phone* and use su to write to the file:

1. adb shell
2. su
3. echo "chrome --sync-url" > /data/local/chrome-command-line

*Rooting an Android phone is actually very easy and takes only a few minutes. There are a number of one click apps for rooting your phone (e.g. KingoRoot). For the case of MotoG, I had to do a few more steps to root, following this)