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

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 54fcad6f2319211e7fb4fc1572cd49861571fc4f..7888a8f70238222dfb1c493b051f860ccd63d546 100644
--- a/base/trace_event/process_memory_dump.cc
+++ b/base/trace_event/process_memory_dump.cc
@@ -35,6 +35,24 @@ MemoryAllocatorDump* ProcessMemoryDump::GetAllocatorDump(
   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 case are not relevant, let's just prevent clients to accidentally

[petrcermak, 2015/05/21 08:17:37]

s/case/cases/, s/to/from/

[Primiano Tucci (use gerrit), 2015/05/21 08:33:46]

Done.

+  // try doing that.

[petrcermak, 2015/05/21 08:17:38]

"try" doesn't belong here (it would have to be "trying"). I'd modify the end of
the whole sentence to: "[...] prevent clients from doing that accidentally."

[Primiano Tucci (use gerrit), 2015/05/21 08:33:46]

Reworded as "trying from doing it" (and I saved one LOC, yay)

+  DCHECK(!other->has_process_totals() && !other->has_process_mmaps());
+
+  // Moves the ownership of all the MemoryAllocatorDump(s) contained in |other|

[petrcermak, 2015/05/21 08:17:37]

nit: I don't think you need "the" in front of "MemoryAllocatorDump(s)".

[Primiano Tucci (use gerrit), 2015/05/21 08:33:46]

Done.

+  // 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_) {