[memory-infra] Add API to ProcessMemoryDump to create ownership edges for base::SharedMemory

base/trace_event/process_memory_dump.h

Index: base/trace_event/process_memory_dump.h
diff --git a/base/trace_event/process_memory_dump.h b/base/trace_event/process_memory_dump.h
index ec82c10cede08db528e050e8b1c58e6f4c41c427..7fdb2dd23a19f9bb9b29adc0b5cee368480d8a61 100644
--- a/base/trace_event/process_memory_dump.h
+++ b/base/trace_event/process_memory_dump.h
@@ -30,6 +30,9 @@
 #endif
 
 namespace base {
+
+class UnguessableToken;
+
 namespace trace_event {
 
 class HeapProfilerSerializationState;
@@ -150,6 +153,32 @@ class BASE_EXPORT ProcessMemoryDump {
                                    const MemoryAllocatorDumpGuid& target,
                                    int importance);
 
+  // Creates ownership edges for memory backed by base::SharedMemory. Handles
+  // the case of cross process sharing and importnace of ownership for the case
+  // with and without the base::SharedMemory dump provider. The new version
+  // should just use global dumps created by SharedMemoryTracker and this
+  // function handles the transition until we get SharedMemory IDs through mojo
+  // channel crbug.com/713763. The weak version creates a weak global dump.
+  // |client_local_dump_guid| The guid of the local dump created by the client
+  // of base::SharedMemory.
+  // |client_global_dump_guid| The global guid given by the clients to create
+  // ownership edges of their own. These global dumps will no longer be required
+  // after the transition.
+  // |shared_memory_guid| The ID of the base::SharedMemory that is assigned
+  // globally, used to create global dump edges in the new model.
+  // |importance| Importance of the global dump edges to say if the current
+  // process owns the memory segment.

[dcheng, 2017/06/08 19:28:30]

I'm not sure what "importance" means still based on this comment. Is this to
help hint which process the shared memory should be counted against?

[ssid, 2017/06/08 19:43:16]

what importance means is explained in the comment on function
AddOwnershipEdge(). "importance of edges" refers to the description in line 141.
That is why I did not explain in further detail here.

Yes you are right about how importance is used.

[dcheng, 2017/06/08 20:40:52]

I see; I didn't see it because that section was collapsed by default in the
Rietveld diff.

[ssid, 2017/06/08 20:43:35]

Or maybe memory-infra is too complicated :P

+  void CreateSharedMemoryOwnershipEdge(
+      const MemoryAllocatorDumpGuid& client_local_dump_guid,
+      const MemoryAllocatorDumpGuid& client_global_dump_guid,
+      const UnguessableToken& shared_memory_guid,
+      int importance);
+  void CreateWeakSharedMemoryOwnershipEdge(
+      const MemoryAllocatorDumpGuid& client_local_dump_guid,
+      const MemoryAllocatorDumpGuid& client_global_dump_guid,
+      const UnguessableToken& shared_memory_guid,
+      int importance);
+
   const AllocatorDumpEdgesMap& allocator_dumps_edges_for_testing() const {
     return allocator_dumps_edges_;
   }
@@ -201,6 +230,13 @@ class BASE_EXPORT ProcessMemoryDump {
   MemoryAllocatorDump* AddAllocatorDumpInternal(
       std::unique_ptr<MemoryAllocatorDump> mad);
 
+  void CreateSharedMemoryOwnershipEdgeInternal(
+      const MemoryAllocatorDumpGuid& client_local_dump_guid,
+      const MemoryAllocatorDumpGuid& client_global_dump_guid,
+      const UnguessableToken& shared_memory_guid,
+      int importance,
+      bool is_weak);

[dcheng, 2017/06/08 19:28:30]

Normally I would suggest using an enum, the bool is pretty unclear

(but maybe this is OK since it's a private helper)

[ssid, 2017/06/08 19:43:16]

Yeah, i feel enum is not required for an internal implementation.

+
   MemoryAllocatorDump* GetBlackHoleMad();
 
   ProcessMemoryTotals process_totals_;