Google search appears out of nowhere
This Google Voice Search pop up appears to be a bug in the Huawei Ascend Y300 model. From  This thread on Android Forums that you are not alone with the issue but there is no resolution in the thread.

Further reading in This modaco thread that it might be related to the headphones causing something in the device to trigger Voice Search rather than the intended result e.g. skipping song, changing volume etc. 

One user (referring to the headphones) states: 


  "I get this all the damn time on my Y300. In my case it's Voice Search that opens (I'm on CM11) and I tried renaming the VoiceSearch.apk in /system/app/ (IIRC) but still it comes up.
  
  It's probably getting the contacts confused and triggering that third button on some headsets, but it's bloody annoying."


The fact he is using CyanogenMod and not the stock ROM suggests a Hardware issue rather than a software one. 

You could attempt to disable Google Voice search while listening to music as a workaround, althought it is part of Search itself and this may be inconvenient on a day to day basis.