[tracing] Add support to pre-load and merge ProcessMemoryDump(s).

base/trace_event/process_memory_dump.cc

 // Copyright 2015 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 "base/trace_event/process_memory_dump.h"
 
 #include "base/trace_event/process_memory_totals.h"
 #include "base/trace_event/trace_event_argument.h"
 
 namespace base {
@@ skipping 17 matching lines @@
   allocator_dumps_[absolute_name] = mad;
   return mad;
 }
 
 MemoryAllocatorDump* ProcessMemoryDump::GetAllocatorDump(
     const std::string& absolute_name) const {
   auto it = allocator_dumps_.find(absolute_name);
   return it == allocator_dumps_.end() ? nullptr : it->second;
 }
 
+void ProcessMemoryDump::TakeAllDumpsFrom(ProcessMemoryDump* other) {
+  // We support only merging of MemoryAllocatorDumps. The special process_totals
+  // and mmaps cases are not relevant, let's just prevent clients from doing it.
+  DCHECK(!other->has_process_totals() && !other->has_process_mmaps());
+
+  // Moves the ownership of all MemoryAllocatorDump(s) contained in |other|
+  // into this ProcessMemoryDump.
+  for (MemoryAllocatorDump* mad : other->allocator_dumps_storage_) {
+    // Check that we don't merge duplicates.
+    DCHECK_EQ(0ul, allocator_dumps_.count(mad->absolute_name()));
+    allocator_dumps_storage_.push_back(mad);
+    allocator_dumps_[mad->absolute_name()] = mad;
+  }
+  other->allocator_dumps_storage_.weak_clear();
+  other->allocator_dumps_.clear();
+}
+
 void ProcessMemoryDump::AsValueInto(TracedValue* value) const {
   // Build up the [dumper name] -> [value] dictionary.
   if (has_process_totals_) {
     value->BeginDictionary("process_totals");
     process_totals_.AsValueInto(value);
     value->EndDictionary();
   }
   if (has_process_mmaps_) {
     value->BeginDictionary("process_mmaps");
     process_mmaps_.AsValueInto(value);
     value->EndDictionary();
   }
   if (allocator_dumps_storage_.size() > 0) {
     value->BeginDictionary("allocators");
     for (const MemoryAllocatorDump* allocator_dump : allocator_dumps_storage_)
       allocator_dump->AsValueInto(value);
     value->EndDictionary();
   }
 }
 
 }  // namespace trace_event
 }  // namespace base