Get chromium's major version directly instead of parsing strings

Getting Chromium's version is not trivial in code and some code
got the version string dynamically during runtime and parsed it.
Since several files defined the same helper function
GetCurrentMajorVersion, those clashed in some extreme
jumbo builds. This drops this function and instead gets the
version directly from the version system via a C/C++ define.

Since the version number now will be compiled into autofill,
it will have to recompile if the major version number changes.

Bug: 907570
Change-Id: I5823d977f3ff58c4b19f173c01031d4a9aa5c56c
Reviewed-on: https://chromium-review.googlesource.com/c/1409548
Reviewed-by: Sebastien Seguin-Gagnon <sebsg@chromium.org>
Commit-Queue: Daniel Bratell <bratell@opera.com>
Cr-Commit-Position: refs/heads/master@{#622490}
5 files changed