clang/win: Fix -Wunused-function warnings after https://codereview.chromium.org/1420003004/

Fixes:

..\..\components/leveldb_proto/proto_database_impl.h(102,6) : error: unused
function 'InitFromTaskRunner' [-Werror,-Wunused-function]
void InitFromTaskRunner(LevelDB* database, const base::FilePath& database_dir,
     ^
..\..\components/leveldb_proto/proto_database_impl.h(110,6) : error: unused
function 'DestroyFromTaskRunner' [-Werror,-Wunused-function]
void DestroyFromTaskRunner(const base::FilePath& database_dir, bool* success) {
     ^

Defining non-inline functions in a .h file generally can't work, so the
warning pointed at bad code here.

BUG=82385
TBR=jianli

Review URL: https://codereview.chromium.org/1422313003 .

Cr-Commit-Position: refs/heads/master@{#356509}
1 file changed