Fix Android build break when is_chrome_branded = true.

Some constexpr static class members still require definitions in C++14 but
it is not clear why this build break occurred on Android only.

Change-Id: I3e0d04d765f02ce37db2f7b4df90bb4d85fcab6d

BUG: 1030716
Change-Id: I3e0d04d765f02ce37db2f7b4df90bb4d85fcab6d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1950749
Reviewed-by: Joshua Pawlicki <waffles@chromium.org>
Commit-Queue: Sorin Jianu <sorin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#721601}