Today Google uploaded a video on Gmail on Google Operating System on Its main YouTube channel, which actually revealed some of Gmail unknown and seems to be upcoming feature. Google Have removed that video from its channel, but we have got a separate source and screen shots below.
Check the video first
New Remarkable Feature:
# A flexible layout that adapts to any window size
# Display density options like in Google Docs
# Resizable chat/labels sections, new high-definition themes
Its still not available, but could be available very soon. Stay tuned in TheTechJournal.com