cc::SurfaceDependencyTracker should not crash when a Display goes away

cc/surfaces/frame_sink_manager.cc

Index: cc/surfaces/frame_sink_manager.cc
diff --git a/cc/surfaces/frame_sink_manager.cc b/cc/surfaces/frame_sink_manager.cc
index c16a921fc47a38413dc4e0724903b8e7171c4815..8b0f21c82eaa543a938fac40856ae25ae8227a50 100644
--- a/cc/surfaces/frame_sink_manager.cc
+++ b/cc/surfaces/frame_sink_manager.cc
@@ -9,6 +9,7 @@
 
 #include "base/logging.h"
 #include "cc/surfaces/frame_sink_manager_client.h"
+#include "cc/surfaces/primary_begin_frame_source.h"
 
 #if DCHECK_IS_ON()
 #include <sstream>
@@ -16,15 +17,14 @@
 
 namespace cc {
 
-FrameSinkManager::FrameSinkSourceMapping::FrameSinkSourceMapping()
-    : source(nullptr) {}
+FrameSinkManager::FrameSinkSourceMapping::FrameSinkSourceMapping() = default;
 
 FrameSinkManager::FrameSinkSourceMapping::FrameSinkSourceMapping(
     const FrameSinkSourceMapping& other) = default;
 
-FrameSinkManager::FrameSinkSourceMapping::~FrameSinkSourceMapping() {}
+FrameSinkManager::FrameSinkSourceMapping::~FrameSinkSourceMapping() = default;
 
-FrameSinkManager::FrameSinkManager() {}
+FrameSinkManager::FrameSinkManager() = default;
 
 FrameSinkManager::~FrameSinkManager() {
   // All CompositorFrameSinks should be unregistered prior to
@@ -73,6 +73,14 @@ void FrameSinkManager::UnregisterFrameSinkManagerClient(
   clients_.erase(client_iter);
 }
 
+std::unique_ptr<BeginFrameSource>
+FrameSinkManager::CreatePrimaryBeginFrameSource() {
+  std::unique_ptr<PrimaryBeginFrameSource> begin_frame_source =
+      base::MakeUnique<PrimaryBeginFrameSource>();
+  begin_frame_source->Init(this);
+  return std::move(begin_frame_source);
+}
+
 void FrameSinkManager::RegisterBeginFrameSource(
     BeginFrameSource* source,
     const FrameSinkId& frame_sink_id) {
@@ -82,6 +90,9 @@ void FrameSinkManager::RegisterBeginFrameSource(
 
   registered_sources_[source] = frame_sink_id;
   RecursivelyAttachBeginFrameSource(frame_sink_id, source);
+
+  for (auto& observer : observer_list_)
+    observer.OnBeginFrameSourceAdded(source);
 }
 
 void FrameSinkManager::UnregisterBeginFrameSource(BeginFrameSource* source) {
@@ -91,6 +102,9 @@ void FrameSinkManager::UnregisterBeginFrameSource(BeginFrameSource* source) {
   FrameSinkId frame_sink_id = registered_sources_[source];
   registered_sources_.erase(source);
 
+  for (auto& observer : observer_list_)
+    observer.OnBeginFrameSourceRemoved(source);
+
   if (frame_sink_source_map_.count(frame_sink_id) == 0u)
     return;
 
@@ -103,6 +117,12 @@ void FrameSinkManager::UnregisterBeginFrameSource(BeginFrameSource* source) {
     RecursivelyAttachBeginFrameSource(source_iter.second, source_iter.first);
 }
 
+BeginFrameSource* FrameSinkManager::GetPrimaryBeginFrameSource() {
+  if (registered_sources_.empty())
+    return nullptr;
+  return registered_sources_.begin()->first;
+}
+
 void FrameSinkManager::RecursivelyAttachBeginFrameSource(
     const FrameSinkId& frame_sink_id,
     BeginFrameSource* source) {