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: refs/heads/master@{#351108}

components/sync_driver.gypi

@@ -157,6 +157,7 @@
         ['configuration_policy==1', {
           'dependencies': [
             'policy',
+            'policy_component',
           ],
           'sources': [
             'sync_driver/sync_policy_handler.cc',