fix(mdPanel): Theming is not initialized on certain panel implementations.

[bradrich]

Actual Behavior:

• What is the issue? * If theming doesn't get initialized on mdPanel components, i.e. mdTooltip, then the color styling falls back to the default mdPanel styling.
• What is the expected behavior? Theming should always be initialized.

CodePen (or steps to reproduce the issue): *

• Before theming problem:
  
• After theming problem:
  

Angular Versions: *

• Angular Version: Latest
• Angular Material Version: Master

Additional Information:

• Browser Type: * All
• Browser Version: * Latest
• OS: * All
• Stack Traces: N/A

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