[Solved]-Docking a detached view with Eclipse-eclipse

From @zvezda's comment above,

"Windows -> Reset Perspective ..."

was the only method that worked for me (using Mars on Fedora 22).

You have to move each tab from the detached views window to the side of a tab in the main window. (The fact that we should move it to the side of another tab was a detail that took me a while to grasp.) A GIF would help:

Note the little green vertical line that appears beside the "Servers" tab — it indicates you've dragged the tab in the right place:

* The red circle only appears when I am pressing the mouse button. It was added by an external program to highlight when the mouse is pressed; it will not appear to you.

As per njol's answer above, once you have your tab detached (showing as floating outside of your Eclipse IDE), simply click on the tab (not on the title of detached tab window) and drag. Then you will see mouse cursor change showing you where you can drop it to attach the tab to IDE.