GitLab

Remove useless class and struct forward declarations, and add
missing ones in base header files.

BUG=662195
CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_precise_blink_rel

Review-Url: https://codereview.chromium.org/2479683004
Cr-Commit-Position: refs/heads/master@{#430160}