[memory-infra] Add method to override importance of ownership edges

base/trace_event/process_memory_dump.cc

Index: base/trace_event/process_memory_dump.cc
diff --git a/base/trace_event/process_memory_dump.cc b/base/trace_event/process_memory_dump.cc
index 9f710936e1405f2b4215761ab0d357d75b7dbd8d..13b3835f9a48855e7c7899e0fd52b410e7d9be36 100644
--- a/base/trace_event/process_memory_dump.cc
+++ b/base/trace_event/process_memory_dump.cc
@@ -286,8 +286,7 @@ void ProcessMemoryDump::TakeAllDumpsFrom(ProcessMemoryDump* other) {
   other->allocator_dumps_.clear();
 
   // Move all the edges.
-  allocator_dumps_edges_.insert(allocator_dumps_edges_.end(),
-                                other->allocator_dumps_edges_.begin(),
+  allocator_dumps_edges_.insert(other->allocator_dumps_edges_.begin(),
                                 other->allocator_dumps_edges_.end());
   other->allocator_dumps_edges_.clear();
 
@@ -326,7 +325,8 @@ void ProcessMemoryDump::AsValueInto(TracedValue* value) const {
   }
 
   value->BeginArray("allocators_graph");
-  for (const MemoryAllocatorDumpEdge& edge : allocator_dumps_edges_) {
+  for (const auto& it : allocator_dumps_edges_) {
+    const MemoryAllocatorDumpEdge& edge = it.second;
     value->BeginDictionary();
     value->SetString("source", edge.source.ToString());
     value->SetString("target", edge.target.ToString());
@@ -340,8 +340,10 @@ void ProcessMemoryDump::AsValueInto(TracedValue* value) const {
 void ProcessMemoryDump::AddOwnershipEdge(const MemoryAllocatorDumpGuid& source,
                                          const MemoryAllocatorDumpGuid& target,
                                          int importance) {
-  allocator_dumps_edges_.push_back(
-      {source, target, importance, kEdgeTypeOwnership});
+  DCHECK(allocator_dumps_edges_.count(source) == 0 ||
+         allocator_dumps_edges_[source].overridable);
+  allocator_dumps_edges_[source] = {
+      source, target, importance, kEdgeTypeOwnership, false /* overridable */};
 }
 
 void ProcessMemoryDump::AddOwnershipEdge(
@@ -350,6 +352,21 @@ void ProcessMemoryDump::AddOwnershipEdge(
   AddOwnershipEdge(source, target, 0 /* importance */);
 }
 
+void ProcessMemoryDump::AddOverridableOwnershipEdge(
+    const MemoryAllocatorDumpGuid& source,
+    const MemoryAllocatorDumpGuid& target,
+    int importance) {
+  if (allocator_dumps_edges_.count(source) == 0) {
+    allocator_dumps_edges_[source] = {
+        source, target, importance, kEdgeTypeOwnership, true /* overridable */};
+  } else {
+    // An edge between the source and target already exits. So, do nothing here
+    // since the new overridable edge is implicitly overridden by a strong edge
+    // which was created earlier.
+    DCHECK(!allocator_dumps_edges_[source].overridable);
+  }
+}
+
 void ProcessMemoryDump::AddSuballocation(const MemoryAllocatorDumpGuid& source,
                                          const std::string& target_node_name) {
   // Do not create new dumps for suballocations in background mode.