Ignore disk cache for concurrent byte range requests to a single resource, to prevent stalling.

net/http/http_cache_transaction.cc

Index: net/http/http_cache_transaction.cc
diff --git a/net/http/http_cache_transaction.cc b/net/http/http_cache_transaction.cc
index 648199063a7e0f032f885a0467296a01ece8b035..a0446f98930df0a3c71c24bd493dc303fc78a6bd 100644
--- a/net/http/http_cache_transaction.cc
+++ b/net/http/http_cache_transaction.cc
@@ -1200,7 +1200,35 @@ int HttpCache::Transaction::DoAddToEntry() {
   net_log_.BeginEvent(NetLog::TYPE_HTTP_CACHE_ADD_TO_ENTRY);
   DCHECK(entry_lock_waiting_since_.is_null());
   entry_lock_waiting_since_ = TimeTicks::Now();
-  return cache_->AddTransactionToEntry(new_entry_, this);
+
+  int result = cache_->AddTransactionToEntry(new_entry_, this);
+
+  // If we're a range request and we're blocked by the reader/writer lock, then
+  // we'll switch to pass-through mode, this eliminates a long-running issue
+  // (crbug.com/31014) where two of the same video resource could not be played
+  // back simultaneously due to one locking the cache entry until the entire
+  // video was downloaded.
+  //
+  // This is not an ideal solution, as we are now ignoring the cache entirely
+  // for all range requests to a resource beyond the first. This is however a
+  // much more succinct solution than the alternatives, which would require
+  // somewhat significant changes to the http caching logic.
+  // TODO(rileya): Support simultaneous transactions on sparse cache entries,
+  // and remove this hack (crbug.com/362215).
+  if (partial_ && result == net::ERR_IO_PENDING && (new_entry_->writer ||
+      (mode() & Transaction::WRITE && !new_entry_->readers.empty()))) {
+    entry_lock_waiting_since_ = TimeTicks();
+    net_log_.EndEvent(NetLog::TYPE_HTTP_CACHE_ADD_TO_ENTRY);
+    mode_ = NONE;
+    partial_->RestoreHeaders(&custom_request_->extra_headers);
+    partial_.reset();
+    next_state_ = STATE_SEND_REQUEST;
+    cache_pending_ = false;
+    cache_->RemovePendingTransaction(this);
+    new_entry_ = NULL;
+    return OK;
+  }
+  return result;
 }
 
 int HttpCache::Transaction::DoAddToEntryComplete(int result) {