remoting: Make conversions from gfx::Point to PointF explicit.
remoting: Make conversions from gfx::Point to PointF explicit.

This implicit conversion operator will be going away. The
ui::EventLocationFromNative() call returns a Point, so we need to
explicitly cast it to a PointF, not just store it in one.

R=wez@chromium.org
BUG=342848

Review URL: https://codereview.chromium.org/1417563003

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#355179}

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