Add more intermediate float-backed types for LineBoxes.
Add more intermediate float-backed types for LineBoxes.

This CL adds FloatPointLineLayoutPoint,
FloatSizeLineLayoutSize, and
FloatRectLineLayoutRect, as described as
part of step 2 in
https://docs.google.com/a/chromium.org/document/d/1fro9Drq78rYBwr6K9CPK-y0TDSVxlBuXl6A54XnKAyE/edit.

These classes may not be 100% complete, and may need
a few additional methods added on in future CLs.

BUG=321237

Review URL: https://codereview.chromium.org/750623003

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@186869 bbb929c8-8fbe-4397-9dbb-9b2b20218538

primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs