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

base/trace_event/memory_allocator_dump.cc

Index: base/trace_event/memory_allocator_dump.cc
diff --git a/base/trace_event/memory_allocator_dump.cc b/base/trace_event/memory_allocator_dump.cc
index 5c5af7ee45842e716b92c5fcf7018641a3bfb023..9688cf665718c41c3b6a452433656180f699beb0 100644
--- a/base/trace_event/memory_allocator_dump.cc
+++ b/base/trace_event/memory_allocator_dump.cc
@@ -24,11 +24,13 @@ const char MemoryAllocatorDump::kUnitsObjects[] = "objects";
 
 MemoryAllocatorDump::MemoryAllocatorDump(const std::string& absolute_name,
                                          ProcessMemoryDump* process_memory_dump,
-                                         const MemoryAllocatorDumpGuid& guid)
+                                         const MemoryAllocatorDumpGuid& guid,
+                                         uint8_t flags)
     : absolute_name_(absolute_name),
       process_memory_dump_(process_memory_dump),
       attributes_(new TracedValue),
-      guid_(guid) {
+      guid_(guid),
+      flags_(flags) {
   // The |absolute_name| cannot be empty.
   DCHECK(!absolute_name.empty());
 
@@ -37,6 +39,14 @@ MemoryAllocatorDump::MemoryAllocatorDump(const std::string& absolute_name,
   DCHECK(absolute_name[0] != '/' && *absolute_name.rbegin() != '/');
 }
 
+MemoryAllocatorDump::MemoryAllocatorDump(const std::string& absolute_name,
+                                         ProcessMemoryDump* process_memory_dump,
+                                         const MemoryAllocatorDumpGuid& guid)
+    : MemoryAllocatorDump(absolute_name,
+                          process_memory_dump,
+                          guid,
+                          0 /* flags */) {}
+
 // If the caller didn't provide a guid, make one up by hashing the
 // absolute_name with the current PID.
 // Rationale: |absolute_name| is already supposed to be unique within a
@@ -48,7 +58,8 @@ MemoryAllocatorDump::MemoryAllocatorDump(const std::string& absolute_name,
                           MemoryAllocatorDumpGuid(StringPrintf(
                               "%d:%s",
                               TraceLog::GetInstance()->process_id(),
-                              absolute_name.c_str()))) {
+                              absolute_name.c_str())),
+                          0 /* flags */) {
   string_conversion_buffer_.reserve(16);
 }
 
@@ -90,6 +101,8 @@ void MemoryAllocatorDump::AsValueInto(TracedValue* value) const {
   value->BeginDictionaryWithCopiedName(absolute_name_);
   value->SetString("guid", guid_.ToString());
   value->SetValue("attrs", *attributes_);
+  if (flags_)
+    value->SetInteger("flags", static_cast<int>(flags_));
   value->EndDictionary();  // "allocator_name/heap_subheap": { ... }
 }