Do not attempt to invalidate cache entries with unpopulated NIKs

If the split cache is enabled, do not attempt to call
DoomMainEntryForUrl if the network_isolation_key (NIK) is unpopulated.
This previously would occur for requests in HttpCacheLookupManager, but
the cache is bypassed for these requests, making the call unnecessary.
When the call was made, a DCHECK was hit in GenerateCacheKey given the
empty NIK.

Bug: 1014077
Change-Id: I566d021d50ea7200d8d99702e382c7db932dfe44
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1860312Reviewed-by: Shivani Sharma <shivanisha@chromium.org>
Commit-Queue: Alex Turner <alexmt@chromium.org>
Cr-Commit-Position: refs/heads/master@{#705988}

net/http/http_cache_transaction.cc

@@ -1817,9 +1817,14 @@ int HttpCache::Transaction::DoSuccessfulSendRequest() {
     DoneWithEntry(true);
   }
 
-  // Invalidate any cached GET with a successful POST.
+  // Invalidate any cached GET with a successful POST. If the network isolation
+  // key isn't populated with the split cache active, there will be nothing to
+  // invalidate in the cache.
   if (!(effective_load_flags_ & LOAD_DISABLE_CACHE) && method_ == "POST" &&
-      NonErrorResponse(new_response_->headers->response_code())) {
+      NonErrorResponse(new_response_->headers->response_code()) &&
+      (!base::FeatureList::IsEnabled(
+           net::features::kSplitCacheByNetworkIsolationKey) ||
+       request_->network_isolation_key.IsFullyPopulated())) {
     cache_->DoomMainEntryForUrl(request_->url, request_->network_isolation_key);
   }