[SimpleCache] Prefetch stream 1 so that the first read is faster

net/disk_cache/simple/simple_entry_impl.cc

Index: net/disk_cache/simple/simple_entry_impl.cc
diff --git a/net/disk_cache/simple/simple_entry_impl.cc b/net/disk_cache/simple/simple_entry_impl.cc
index 62347507f8d8d61b2e272901670212bbe5399cbf..41a05a52b4e433769447799ccfa7de7476c6d82e 100644
--- a/net/disk_cache/simple/simple_entry_impl.cc
+++ b/net/disk_cache/simple/simple_entry_impl.cc
@@ -196,7 +196,8 @@ SimpleEntryImpl::SimpleEntryImpl(net::CacheType cache_type,
       net_log_(
           net::NetLogWithSource::Make(net_log,
                                       net::NetLogSourceType::DISK_CACHE_ENTRY)),
-      stream_0_data_(new net::GrowableIOBuffer()) {
+      stream_0_data_(new net::GrowableIOBuffer()),
+      stream_1_prefetch_data_(new net::GrowableIOBuffer()) {
   static_assert(arraysize(data_size_) == arraysize(crc32s_end_offset_),
                 "arrays should be the same size");
   static_assert(arraysize(data_size_) == arraysize(crc32s_),
@@ -557,7 +558,8 @@ size_t SimpleEntryImpl::EstimateMemoryUsage() const {
   return sizeof(SimpleSynchronousEntry) +
          base::trace_event::EstimateMemoryUsage(pending_operations_) +
          base::trace_event::EstimateMemoryUsage(executing_operation_) +
-         (stream_0_data_ ? stream_0_data_->capacity() : 0);
+         (stream_0_data_ ? stream_0_data_->capacity() : 0) +
+         (stream_1_prefetch_data_ ? stream_1_prefetch_data_->capacity() : 0);
 }
 
 SimpleEntryImpl::~SimpleEntryImpl() {
@@ -866,6 +868,8 @@ void SimpleEntryImpl::ReadDataInternal(int stream_index,
     return;
   }
 
+  // XXX(jkarlin): See if we can use the prefetch data for stream 1.
+
   state_ = STATE_IO_PENDING;
   if (!doomed_ && backend_.get())
     backend_->index()->UseIfExists(entry_hash_);
@@ -1161,6 +1165,10 @@ void SimpleEntryImpl::CreationOperationComplete(
     crc32s_[0] = in_results->stream_0_crc32;
     crc32s_end_offset_[0] = in_results->entry_stat.data_size(0);
   }
+  if (in_results->stream_1_prefetch_data.get()) {
+    stream_1_prefetch_data_ = in_results->stream_1_prefetch_data;
+  }
+
   // If this entry was opened by hash, key_ could still be empty. If so, update
   // it with the key read from the synchronous entry.
   if (key_.empty()) {