[ios][PhishGuard] Add buildflag around GetDomFeatures

This CL makes it easier/clearer to split up PasswordProtectionRequest
in a future CL.

GetDomFeatures should be wrapped in a SAFE_BROWSING_AVAILABLE buildflag
since it's declaration is wrapped in that buildflag.

Bug: 1147967
Change-Id: I4a06732c97ba49ad1212816bd073b6e526b29ae4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2638242
Commit-Queue: edchin <edchin@chromium.org>
Reviewed-by: Ali Juma <ajuma@chromium.org>
Reviewed-by: Bettina Dea <bdea@chromium.org>
Cr-Commit-Position: refs/heads/master@{#845514}

components/safe_browsing/content/password_protection/password_protection_request.cc

@@ -338,7 +338,9 @@ void PasswordProtectionRequest::FillRequestProto(bool is_sampled_ping) {
   }
 
   if (IsClientSideDetectionEnabled()) {
+#if BUILDFLAG(SAFE_BROWSING_AVAILABLE)
     GetDomFeatures();
+#endif  // BUILDFLAG(SAFE_BROWSING_AVAILABLE)
   } else {
     SendRequest();
   }