[Extensions] Add missing include

Fix failure from crrev.com/2097de33a1f3d04e78d93e9e2f16aad4b97e47d7

BUG=665517
BUG=660498

Review-Url: https://codereview.chromium.org/2502063002
Cr-Commit-Position: refs/heads/master@{#432274}
(cherry picked from commit 6c0d227bc9eae0114258f6ad1e00973dda4d424d)

Review URL: https://codereview.chromium.org/2504513003 .

Cr-Commit-Position: refs/branch-heads/2883@{#579}
Cr-Branched-From: 614d31daee2f61b0180df403a8ad43f20b9f6dd7-refs/heads/master@{#423768}
1 file changed