Cannot complete the install because one or more required items could not be found.
  Software being installed: Android Development Tools 8.0.1.v201012062107-82219 (com.android.ide.eclipse.adt.feature.group 8.0.1.v201012062107-82219)
  Missing requirement: Android Development Tools 8.0.1.v201012062107-82219 (com.android.ide.eclipse.adt.feature.group 8.0.1.v201012062107-82219) requires 'org.eclipse.gef 0.0.0' but it could not be found

So I added this update into Eclipse by
1. Go to the menu 'Help',
2. Choose 'Install New Software',
3. Place the GEF SDK updates URL into the box

http://download.eclipse.org/tools/gef/updates/releases/

after 'Work with:',
4. Choose the right version of updates in the box below (for me, GEF SDK 3.5.1),
5. Click 'Next',
6. After Eclipse calculates all the dependencies, just click 'Finish' and let it install the plugin.

Pour erreur "org.eclipse.wst.sse.core 0.0.0"