[iOS] Fetch iOS-specific instead of macOS-specific Safe Browsing lists

This CL makes us use iOS-specific Safe Browsing lists on iOS.

Bug: 1028755
Change-Id: I675531f4f2fe155a0480ca31e36d7ceb21122b20
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2121048Reviewed-by: Varun Khaneja <vakh@chromium.org>
Commit-Queue: Ali Juma <ajuma@chromium.org>
Cr-Commit-Position: refs/heads/master@{#753596}

components/safe_browsing/core/db/v4_protocol_manager_util.cc

@@ -118,6 +118,8 @@ PlatformType GetCurrentPlatformType() {
   return WINDOWS_PLATFORM;
 #elif defined(OS_LINUX)
   return LINUX_PLATFORM;
+#elif defined(OS_IOS)
+  return IOS_PLATFORM;
 #elif defined(OS_MACOSX)
   return OSX_PLATFORM;
 #else