Change VirtualTimePolicy::PAUSE_IF_NETWORK_FETCHES_PENDING

components/scheduler/renderer/web_view_scheduler_impl.cc

Index: components/scheduler/renderer/web_view_scheduler_impl.cc
diff --git a/components/scheduler/renderer/web_view_scheduler_impl.cc b/components/scheduler/renderer/web_view_scheduler_impl.cc
index da4e80b30b6fdcd2655f330e39d74d0bfb386137..0e41a26bbf4bdaabd7fa0062a055cd9d7a4c3b00 100644
--- a/components/scheduler/renderer/web_view_scheduler_impl.cc
+++ b/components/scheduler/renderer/web_view_scheduler_impl.cc
@@ -5,6 +5,7 @@
 #include "components/scheduler/renderer/web_view_scheduler_impl.h"
 
 #include "base/logging.h"
+#include "components/scheduler/base/real_time_domain.h"
 #include "components/scheduler/base/virtual_time_domain.h"
 #include "components/scheduler/child/scheduler_tqm_delegate.h"
 #include "components/scheduler/renderer/auto_advancing_virtual_time_domain.h"
@@ -27,7 +28,8 @@ WebViewSchedulerImpl::WebViewSchedulerImpl(
       virtual_time_policy_(VirtualTimePolicy::ADVANCE),
       page_visible_(true),
       disable_background_timer_throttling_(disable_background_timer_throttling),
-      allow_virtual_time_to_advance_(true) {
+      allow_virtual_time_to_advance_(true),
+      have_seen_loading_task_(false) {
   renderer_scheduler->AddWebViewScheduler(this);
 }
 
@@ -38,8 +40,14 @@ WebViewSchedulerImpl::~WebViewSchedulerImpl() {
     frame_scheduler->DetachFromWebViewScheduler();
   }
   renderer_scheduler_->RemoveWebViewScheduler(this);
-  if (virtual_time_domain_)
+  if (virtual_time_domain_) {
+    // Since we're just about to delete virtual_time_domain_ we'd better move
+    // the per-thread task queues back to the RealTimeDomain or we risk a UAF
+    // when the task queues get deleted.
+    renderer_scheduler_->SetPerThreadTaskRunnerTimeDomain(
+        renderer_scheduler_->real_time_domain());
     renderer_scheduler_->UnregisterTimeDomain(virtual_time_domain_.get());
+  }
 }
 
 void WebViewSchedulerImpl::setPageVisible(bool page_visible) {
@@ -98,6 +106,10 @@ void WebViewSchedulerImpl::enableVirtualTime() {
   for (WebFrameSchedulerImpl* frame_scheduler : frame_schedulers_) {
     frame_scheduler->OnVirtualTimeDomainChanged();
   }
+
+  // For determinism the per-thread task queues must use virtual time too.
+  renderer_scheduler_->SetPerThreadTaskRunnerTimeDomain(
+        virtual_time_domain_.get());
 }
 
 void WebViewSchedulerImpl::setAllowVirtualTimeToAdvance(
@@ -119,6 +131,7 @@ bool WebViewSchedulerImpl::virtualTimeAllowedToAdvance() const {
 
 void WebViewSchedulerImpl::DidStartLoading(unsigned long identifier) {
   pending_loads_.insert(identifier);
+  have_seen_loading_task_ = true;
 
   if (virtual_time_policy_ !=
       VirtualTimePolicy::PAUSE_IF_NETWORK_FETCHES_PENDING) {
@@ -154,7 +167,11 @@ void WebViewSchedulerImpl::setVirtualTimePolicy(VirtualTimePolicy policy) {
       break;
 
     case VirtualTimePolicy::PAUSE_IF_NETWORK_FETCHES_PENDING:
-      setAllowVirtualTimeToAdvance(pending_loads_.size() == 0);
+      // We pause virtual time until we've seen a loading task posted, because
+      // otherwise we could advance virtual time arbitarially far before the
+      // first load arrives.
+      setAllowVirtualTimeToAdvance(pending_loads_.size() == 0 &&
+                                   have_seen_loading_task_);
       break;
   }
 }