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 88c9c857d55e21cb6b8017de3f08821b32cf8964..0a47029bb667cda2b25baf6f4d03c8fbe5c36c81 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/cross_site_resource_handler.h"
 #include "content/browser/loader/resource_loader_delegate.h"
@@ -64,6 +66,10 @@ void PopulateResourceResponse(net::URLRequest* request,
 
 }  // namespace
 
+// The time in ms to delay a cancel of a prefetch unless otherwise specified
+// by a flag.
+static const int kDefaultDelayPrefetchCancelMs = 60000;
+
 ResourceLoader::ResourceLoader(scoped_ptr<net::URLRequest> request,
                                scoped_ptr<ResourceHandler> handler,
                                ResourceLoaderDelegate* delegate)
@@ -458,6 +464,31 @@ void ResourceLoader::StartRequestInternal() {
   delegate_->DidStartRequest(this);
 }
 
+bool ResourceLoader::DelayCancelForPrefetch(const ResourceRequestInfoImpl& info,

[asanka, 2013/10/11 21:01:20]

Can you explain the rationale for this logic? Why is the cancel delayed?

[jkarlin2, 2013/10/14 14:30:00]

Done.

+                                            bool from_renderer) {
+  // Delay requests to cancel prefetches
+  const CommandLine& command_line = *CommandLine::ForCurrentProcess();
+
+  if (from_renderer && !prefetch_timer_ &&
+      info.GetResourceType() == ResourceType::PREFETCH &&
+      command_line.HasSwitch(switches::kDelayPrefetchCancellation)) {
+    // 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 = kDefaultDelayPrefetchCancelMs;
+    }
+
+    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();
 
@@ -469,6 +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();