[tracing] Add method to create "weak" global dumps

base/trace_event/memory_allocator_dump.h

Index: base/trace_event/memory_allocator_dump.h
diff --git a/base/trace_event/memory_allocator_dump.h b/base/trace_event/memory_allocator_dump.h
index 6c514fa6a62380b9ec6180792451a40b3a9dbbf9..0b4821ac58a4c7cf75e8c2d914996902b751802e 100644
--- a/base/trace_event/memory_allocator_dump.h
+++ b/base/trace_event/memory_allocator_dump.h
@@ -26,6 +26,12 @@ class TracedValue;
 // Data model for user-land memory allocator dumps.
 class BASE_EXPORT MemoryAllocatorDump {
  public:
+  enum Flag {

[Primiano Tucci (use gerrit), 2016/01/19 17:07:11]

s/Flag/Flags/

[ssid, 2016/01/20 18:58:34]

Done.

+    // A dump marked weak will be removed from tracing. It is used when dump

[Primiano Tucci (use gerrit), 2016/01/19 17:07:11]

I'd clarify and say "will be discarded by TraceViewer" instead of "will be
removed from tracing".
I'd remove the "It is used when..." part as adds IMHO more confusion.

[ssid, 2016/01/20 18:58:34]

Done.

+    // provider is unsure of the existence of a block of memory.
+    WEAK = 1 << 0,
+  };
+
   // MemoryAllocatorDump is owned by ProcessMemoryDump.
   MemoryAllocatorDump(const std::string& absolute_name,
                       ProcessMemoryDump* process_memory_dump,
@@ -68,6 +74,11 @@ class BASE_EXPORT MemoryAllocatorDump {
     return process_memory_dump_;
   }
 
+  // Use enum Flag to set values.
+  void set_flags(uint8_t flags) { flags_ |= flags; }

[Primiano Tucci (use gerrit), 2016/01/19 17:07:11]

Why not just int (there seems to be lot of precedent in the codebase)? After all
is not going to really save those 24 bits :)

[ssid, 2016/01/20 18:58:34]

Done.

+  void unset_flags(uint8_t flags) { flags_ &= ~flags; }

[Primiano Tucci (use gerrit), 2016/01/19 17:07:11]

s/unset/clear/

[ssid, 2016/01/20 18:58:34]

Done.

+  uint8_t flags() { return flags_; }
+
   // |guid| is an optional global dump identifier, unique across all processes
   // within the scope of a global dump. It is only required when using the
   // graph APIs (see TODO_method_name) to express retention / suballocation or
@@ -83,6 +94,7 @@ class BASE_EXPORT MemoryAllocatorDump {
   ProcessMemoryDump* const process_memory_dump_;  // Not owned (PMD owns this).
   scoped_refptr<TracedValue> attributes_;
   MemoryAllocatorDumpGuid guid_;
+  uint8_t flags_;  // See enum Flag.

[Primiano Tucci (use gerrit), 2016/01/19 17:07:11]

ditto here for int

[ssid, 2016/01/20 18:58:34]

Done.

 
   // A local buffer for Sprintf conversion on fastpath. Avoids allocating
   // temporary strings on each AddScalar() call.