Surfaces: Allow parent to refer to child surfaces that don't exist yet.

cc/surfaces/surface_manager.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/surfaces/surface_manager.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <queue>
@@ skipping 138 matching lines @@
   DCHECK_EQ(lifetime_type_, LifetimeType::REFERENCES);
 
   // Check some conditions that should never happen. We don't want to crash on
   // bad input from a compromised client so just return early.
   if (parent_id.frame_sink_id() == child_id.frame_sink_id()) {
     DLOG(ERROR) << "Cannot add self reference from " << parent_id << " to "
                 << child_id;
     return;
   }
 
-  // We trust that |parent_id| either exists or is about to exist, since is not
-  // sent over IPC. We don't trust |child_id|, since it is sent over IPC.
-  if (surface_map_.count(child_id) == 0) {
-    DLOG(ERROR) << "No surface in map for " << child_id.ToString();
-    return;
-  }
-
   // There could be a temporary reference to |child_id| which we should now
   // remove because a real reference is being added to it. To find out whether
   // or not a temporary reference exists, we need to first look up the
   // FrameSinkId of |child_id| in |temp_references_|, which returns a vector of
   // LocalSurfaceIds, and then search for the LocalSurfaceId of |child_id| in
-  // the
-  // said vector. If there is no temporary reference, we can immediately add the
-  // reference from |parent_id| and return.
+  // the said vector. If there is no temporary reference, we can immediately add
+  // the reference from |parent_id| and return.
   auto refs_iter = temp_references_.find(child_id.frame_sink_id());
   if (refs_iter == temp_references_.end()) {
     AddSurfaceReferenceImpl(parent_id, child_id);
     return;
   }
   std::vector<LocalSurfaceId>& refs = refs_iter->second;
   auto temp_ref_iter =
       std::find(refs.begin(), refs.end(), child_id.local_surface_id());
   if (temp_ref_iter == refs.end()) {
     AddSurfaceReferenceImpl(parent_id, child_id);
@@ skipping 391 matching lines @@
   bool changed = false;
   for (auto& observer : observer_list_)
     observer.OnSurfaceDamaged(surface_id, &changed);
   return changed;
 }
 
 void SurfaceManager::SurfaceCreated(const SurfaceInfo& surface_info) {
   CHECK(thread_checker_.CalledOnValidThread());
 
   if (lifetime_type_ == LifetimeType::REFERENCES) {
-    // We can get into a situation where multiple CompositorFrames arrive for a
-    // CompositorFrameSink before the client can add any references for the
+    // We can get into a situation where multiple CompositorFrames arrive for
+    // a CompositorFrameSink before the client can add any references for the
     // frame. When the second frame with a new size arrives, the first will be
     // destroyed in SurfaceFactory and then if there are no references it will
-    // be deleted during surface GC. A temporary reference, removed when a real
-    // reference is received, is added to prevent this from happening.
-    AddSurfaceReferenceImpl(GetRootSurfaceId(), surface_info.id());
-    temp_references_[surface_info.id().frame_sink_id()].push_back(
-        surface_info.id().local_surface_id());
+    // be deleted during surface GC. A temporary reference, removed when a
+    // real reference is received, is added to prevent this from happening.
+    bool has_real_reference = child_to_parent_refs_.find(surface_info.id()) !=

[kylechar, 2017/02/10 19:51:27]

It's a map from SurfaceId -> unordered_set<SurfaceId>. You're only checking a
set exists. It could be an empty set, so 0 references.

[Fady Samuel, 2017/02/10 20:39:10]

Done.

+                              child_to_parent_refs_.end();
+    if (!has_real_reference) {
+      AddSurfaceReferenceImpl(GetRootSurfaceId(), surface_info.id());
+      temp_references_[surface_info.id().frame_sink_id()].push_back(
+          surface_info.id().local_surface_id());
+    }
   }
 
   for (auto& observer : observer_list_)
     observer.OnSurfaceCreated(surface_info);
 }
 
 #if DCHECK_IS_ON()
 void SurfaceManager::SurfaceReferencesToStringImpl(const SurfaceId& surface_id,
                                                    std::string indent,
                                                    std::stringstream* str) {
@@ skipping 31 matching lines @@
     std::vector<SurfaceId> children(iter->second.begin(), iter->second.end());
     std::sort(children.begin(), children.end());
 
     for (const SurfaceId& child_id : children)
       SurfaceReferencesToStringImpl(child_id, indent + "  ", str);
   }
 }
 #endif  // DCHECK_IS_ON()
 
 }  // namespace cc