Timeline track frames zoom in to max upon resizing Timeline window.

Steps to reproduce:
1. Create a new project.
2. Go to > Window > Sequencing > Timeline.
3. Click on Main Camera game object.
4. Click on Create button in the Timeline window.
5. Click on 'Save' to save the timeline.
6. Shrink timeline window till only the track list is visible then expand it.

Note:
1. Video is attached for the reference.
2. Occurring with both scenarios, docking and undocking timeline window.

Actual result:
Timeline track zoom in at highest upon resizing Timeline window.

Expected result:
Timeline track frames do not zoom-in/zoom-out when window resized.

Reproducible in:
2019.2.0a12, 2019.1.0f2, 2019.1.0a10

Not reproducible in:
2019.1.0a9, 2018.3.0f2

Occurring with package version: 1.0.0

Environment:
Windows and Mac