Add missing dependency of sync_driver on policy_component.
Add missing dependency of sync_driver on policy_component.

SyncPolicyHandler depends on policy::TypeCheckingPolicyHandler which is
included in policy_component target.
GYP missed the dependency while BUILD.gn has it correctly.

BUG=

Review URL: https://codereview.chromium.org/1371743003

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#351108}

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