Move macro to util file (storage/browser)

When building using jumbo, files gets merged
together and macros with the same name may
end up in the same namspace and conflict. This
happens for the macro UMA_HISTOGRAM_MBYTES.

This commit solves the issue by moving
the macro to a shared util file.

Bug: 871163
Change-Id: If3af541913a6add55ce739eb43f5a747cf4afd9a
Reviewed-on: https://chromium-review.googlesource.com/1163602
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Commit-Queue: Oscar Johansson <oscarj@opera.com>
Cr-Commit-Position: refs/heads/master@{#581192}
5 files changed