Fix errors C2238, C2248 and C2059 on MSVC bots.
Fix errors C2238, C2248 and C2059 on MSVC bots.

This CL fixes the following errors on MSVC bots:

../../rtc_base/units/unit_base_unittest.cc(42): error C2059:
  syntax error: '<'

../../rtc_base/units/unit_base_unittest.cc(42): error C2238:
  unexpected token(s) preceding ';'

../..\rtc_base/units/unit_base.h(39): error C2248:
  'webrtc::`anonymous-namespace'::TestUnit::TestUnit':
  cannot access protected member declared in class
  'webrtc::`anonymous-namespace'::TestUnit'

No-Try: True
Bug: None
Change-Id: Ic63a75132107381474aca2e1d42ba96d1f6a1c00
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/172621
Commit-Queue: Mirko Bonadei <d2c43c210eae6feef04f53bae50885e8152edcca@webrtc.org>
Reviewed-by: Karl Wiberg <2c708eb0a58047bf403399f50b3da33ffd2dd444@webrtc.org>
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#30972}

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