[tracing] Fix MemoryDumpManager periodic scheduler and improve tests

base/trace_event/malloc_dump_provider.cc

Index: base/trace_event/malloc_dump_provider.cc
diff --git a/base/trace_event/malloc_dump_provider.cc b/base/trace_event/malloc_dump_provider.cc
index 224b905e4f1ab8f052727c55c45928860eaa4dbb..28aa140d6702bb61c55dab49ae3be6c196078b94 100644
--- a/base/trace_event/malloc_dump_provider.cc
+++ b/base/trace_event/malloc_dump_provider.cc
@@ -39,7 +39,7 @@ bool MallocDumpProvider::OnMemoryDump(const MemoryDumpArgs& args,
   // dlmalloc the total is given by |arena| + |hblkhd|.
   // For more details see link: http://goo.gl/fMR8lF.
   MemoryAllocatorDump* outer_dump = pmd->CreateAllocatorDump("malloc");
-  outer_dump->AddScalar("heap_virtual_size",
+  outer_dump->AddScalar("virtual_size",
                         MemoryAllocatorDump::kUnitsBytes,
                         info.arena + info.hblkhd);