Remove mode assumptions from HttpCache::DoneWithResponseHeaders

Since multiple transactions can now be added to Writers, those transactions will have a WRITE
bit set. Thus remove the DCHECKS that assume otherwise in HttpCache::DoneWithResponseHeaders.

Bug: 750725
Cq-Include-Trybots: master.tryserver.chromium.android:android_cronet_tester;master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: I791177522956ca23d6702254bbf7ee0b25c83bdf
Reviewed-on: https://chromium-review.googlesource.com/760540Reviewed-by: Randy Smith <rdsmith@chromium.org>
Commit-Queue: Shivani Sharma <shivanisha@chromium.org>
Cr-Commit-Position: refs/heads/master@{#515459}

net/http/http_cache.cc

@@ -843,28 +843,12 @@ int HttpCache::DoneWithResponseHeaders(ActiveEntry* entry,
   // through done_headers_queue for performance benefit. (Also, in case of
   // writer transaction, the consumer sometimes depend on synchronous behaviour
   // e.g. while computing raw headers size. (crbug.com/711766))
-  if (transaction->mode() & Transaction::WRITE) {
-    // Partial requests may have write mode even when there is a writer present
-    // since they may be reader for a particular range and writer for another
-    // range.
-    if (!is_partial) {
-      // TODO(crbug.com/750725)
-      DCHECK(!entry->writers || entry->writers->CanAddWriters());
-      DCHECK(entry->done_headers_queue.empty());
-    }
-
-    if (!entry->writers) {
-      AddTransactionToWriters(entry, transaction);
-      ProcessQueuedTransactions(entry);
-      return OK;
-    }
+  if ((transaction->mode() & Transaction::WRITE) && !entry->writers) {
+    AddTransactionToWriters(entry, transaction);
+    ProcessQueuedTransactions(entry);
+    return OK;
   }
 
-  // If this is not the first transaction in done_headers_queue, it should be a
-  // read-mode transaction except if it is a partial request.
-  DCHECK(is_partial || (entry->done_headers_queue.empty() ||
-                        !(transaction->mode() & Transaction::WRITE)));
-
   entry->done_headers_queue.push_back(transaction);
   ProcessQueuedTransactions(entry);
   return ERR_IO_PENDING;