Fixing names of password_manager kEnableManualFallbacksFilling feature.

Fixing  names of password_manager kEnableManualFallbacksFilling feature
as per the naming convention.

Bug: 785953
Change-Id: I4a4baa1649fe9f02c3783a5e4c40bc75e717cc03
Reviewed-on: https://chromium-review.googlesource.com/900566
Reviewed-by: Vaclav Brozek <vabr@chromium.org>
Commit-Queue: NIKHIL SAHNI <nikhil.sahni@samsung.com>
Cr-Commit-Position: refs/heads/master@{#534923}
autofill::AutofillDriver* PasswordAutofillManager::GetAutofillDriver() {
  return password_manager_driver_->GetAutofillDriver();
}

autofill::AutofillDriver* PasswordAutofillManager::GetAutofillDriver() {
  return password_manager_driver_->GetAutofillDriver();
}
