Avoid unexpected results by using unitless line-height

Inheritance of unit specified line-heights does not work as one might
expect.  In some browsers line height is inherited as either unitless
or in pixels. The result is that an inherited line height that was
specified in em is no longer tied to the font size.  Unitless line-height
is the same size as em, but is inherited unitless and applies to the
local font size.

Change-Id: I5359f0c22f2aea70f72c4999b104f965d72bac2d
Merge "Avoid unexpected results by using unitless line-height"