Replace Length::SetValue with assignment

In an effort to "hide" LengthType constants so that those constants
can be moved without much code churn, I noticed that the five different
Length::SetValue functions were barely used and offered no
substantial improvement over a pure assignment so let's keep the
code simple and just use the assignment.

Depending on the compiler and the optimizer, it may generate the
same code, but Android code size changed by a couple of bytes so
probably not.

Change-Id: I691dd8e0df965a87edcd964021faa6f264aa01e5
Reviewed-on: https://chromium-review.googlesource.com/c/1472692
Reviewed-by: Emil A Eklund <eae@chromium.org>
Commit-Queue: Daniel Bratell <bratell@opera.com>
Cr-Commit-Position: refs/heads/master@{#632563}
8 files changed