Allows prefetch requests to live beyond the renderer by delaying

content/browser/loader/resource_loader.cc

Index: content/browser/loader/resource_loader.cc
diff --git a/content/browser/loader/resource_loader.cc b/content/browser/loader/resource_loader.cc
index c99fe5b0d7cd36eb1f45ac2464bdc287ffef3b73..00c3c1a147b31ecb9f91477ce691cc19c86651e3 100644
--- a/content/browser/loader/resource_loader.cc
+++ b/content/browser/loader/resource_loader.cc
@@ -7,7 +7,9 @@
 #include "base/command_line.h"
 #include "base/message_loop/message_loop.h"
 #include "base/metrics/histogram.h"
+#include "base/strings/string_number_conversions.h"
 #include "base/time/time.h"
+#include "base/timer/timer.h"
 #include "content/browser/child_process_security_policy_impl.h"
 #include "content/browser/loader/resource_loader_delegate.h"
 #include "content/browser/loader/resource_request_info_impl.h"
@@ -62,6 +64,8 @@ void PopulateResourceResponse(net::URLRequest* request,
 
 }  // namespace
 
+int ResourceLoader::default_delay_prefetch_cancel_ms_ = 60000;
+
 ResourceLoader::ResourceLoader(scoped_ptr<net::URLRequest> request,
                                scoped_ptr<ResourceHandler> handler,
                                ResourceLoaderDelegate* delegate)
@@ -456,6 +460,35 @@ void ResourceLoader::StartRequestInternal() {
   delegate_->DidStartRequest(this);
 }
 
+bool ResourceLoader::DelayCancelForPrefetch(const ResourceRequestInfoImpl& info,
+                                            bool from_renderer) {
+  // Delay requests to cancel prefetches
+  const CommandLine& command_line = *CommandLine::ForCurrentProcess();
+  if (from_renderer &&
+      command_line.HasSwitch(switches::kDelayPrefetchCancellation) &&
+      info.GetResourceType() == ResourceType::PREFETCH) {

[mmenke, 2013/10/08 14:50:54]

Know it doesn't really matter, but seems like checking the resource type should
go before doing a search through the map of command line flags, for performance
reasons.

[jkarlin2, 2013/10/09 14:44:33]

Done.

+    if (prefetch_timer_.get() && prefetch_timer_->IsRunning()) {

[mmenke, 2013/10/08 14:50:54]

If something is impossible, should we be checking it?  Seems like we should just
DCHECK(prefetch_timer_->IsRunning()) here instead.

[jkarlin2, 2013/10/09 14:44:33]

Done.

+      // We've already processed a cancel for this prefetch, ignore this cancel.
+      return true;
+    } else if (!prefetch_timer_.get()) {

[mmenke, 2013/10/08 14:50:54]

nit:  Here and just above, believe "if (!prefetch_timer_)" is the preferred form
(No get).  Since we support it, may as well use it.

+      // Our first call to cancel this prefetch, start a delay timer.
+      prefetch_timer_.reset(new base::OneShotTimer<ResourceLoader>());
+
+      int delay_ms;
+      if (!base::StringToInt(command_line.GetSwitchValueASCII(
+                                 switches::kDelayPrefetchCancellation),
+                             &delay_ms)) {
+        delay_ms = default_delay_prefetch_cancel_ms_;
+      }
+
+      prefetch_timer_->Start(FROM_HERE, TimeDelta::FromMilliseconds(delay_ms),
+                             this, &ResourceLoader::Cancel);
+      return true;
+    }
+  }
+  return false;
+}
+
 void ResourceLoader::CancelRequestInternal(int error, bool from_renderer) {
   VLOG(1) << "CancelRequestInternal: " << request_->url().spec();
 
@@ -467,6 +500,10 @@ void ResourceLoader::CancelRequestInternal(int error, bool from_renderer) {
   if (from_renderer && (info->is_download() || info->is_stream()))
     return;
 
+  if (DelayCancelForPrefetch(*info, from_renderer)) {
+    return;
+  }
+
   // TODO(darin): Perhaps we should really be looking to see if the status is
   // IO_PENDING?
   bool was_pending = request_->is_pending();