Bug report

Bug summary
When a plot title/label consists of multiple lines (with some mathematics elements that require more vertical space), constrained_layout seems to not work correctly.

Code for reproduction

import matplotlib.pyplot as plt
fig, ax = plt.subplots(figsize=(3, 3), constrained_layout=True)
ax.set_title('First line \n'+r'Second line $\frac{x}{y}$')
ax.set_ylabel('ylabel')
ax.set_xlabel('xlabel')
fig.savefig('constrained_layout_issue.png')

Actual outcome

For now, I am avoiding this issue by increasing h_pad with plt.rcParams['figure.constrained_layout.h_pad'] = 6/72. But this doesn't feel right (there is a lot more blank space left at the bottom of the plot).

Matplotlib version

• Operating system: Mac OS
• Matplotlib version: 3.0.3
• Matplotlib backend (print(matplotlib.get_backend())):
• Python version: 3.7.3
• Jupyter version (if applicable):
• Other libraries: