Partition my HD with Disk Utility, cannot resize the partition WITHOUT installing Windows. WTF? I am installing Ubuntu on my Mac to exist as in parallel with OS X Yosemite, version 1010.3. The screenshot looks similar to previous questions, e.g. How can I resize a partition with Disk Utility?

However, the GUI for Disk Utility does not give me access to resize my partition. Normally, you can click the righthand bottom corner of the volume and drag. I do not have that option---there are no three lines in the bottom righthand for the cursor to drag. 

I cannot manually change the size of the partition in the "Size" box. Normally, you could click/highlight the values and change them. I cannot. The text is "faded". 

Why doesn't the Disk Utility GUI allow me to choose the size of the partition? Should I just do this via the Command Line? 

EDIT: Doesn't anyone else think it's weird that Apple (via Yosemite) forces you to download Windows if you want to partition your hard drive correctly? Note to Apple: FIX THIS!!!
Here are instructions for undoing a Core Storage conversion (source - this method worked for me). It should be non-destructive, but as always, take a backup first! 


Boot into Recovery HD. If for any reason you don't have Recovery HD, then you'll have to make a bootable Yosemite drive and boot into that.
In the Menu Bar, select Utilities > Terminal.
Run diskutil cs list. You'll get an output that looks like this (credits to the Ask Different user in my source):






Select your Logical Volume ID (the one highlighted in the screenshot) and copy it to the clipboard.
Run the Terminal command diskutil cs revert Paste-Your-Logical-Volume-ID-Here.
Run diskutil cs list to verify that your computer can't find any CS volumes.
You're done! Now Disk Utility should be able to do everything you need it to do to your HD!