How I fixed bootloop on my Nexus without loosing data

I was playing around with framework-res.apk and SystemUI.apk to get Ambient Display on my Nexus 4. When I restarted my phone, it seemed to have stuck in a bootloop. I knew that factory reset might've worked. But I didn't want to lose any data.

Fortunately adb was working. When I did adb logcat , it was logging an error saying:
 /system/framework/framework-res.apk is neither a file nor a folder (type=0)

I realized that there was some problem with permissions of that file. I used adb shell and changed the permission of framework-res.apk and SystemUI.apk to 0644. But this was of no use. However I came to know that if I could somehow reset /system partition the problem would be solved.

• So I downloaded the factory image of my phone. For nexus devices it is available here. 
• Extract the contents of the image-xxxx-xxxx.zip to get the file system.img.
• Then ran the following:
  adb reboot bootloader
  fastboot flash system system.img
• This will wipe the /system partition and reset it without touching any other partitions. Hence you will not lose any data.
• Restart. It took a while to start the phone completely. But it solved the problem!

This is how I was able to reset my framework-res.apk and SystemUI.apk!