memory-infra: Start disentangling tracing from memory-infra

Starts refactoring the tracing specific code from MemoryDumpManager
into a new class MemoryTracingObserver. This shouldn't change the
behaviour of the MemoryDumpManager.

BUG=703184

Review-Url: https://codereview.chromium.org/2820433005
Cr-Original-Commit-Position: refs/heads/master@{#466936}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 4a4589fc42e386ba9b2ad1c153d17dd8180941f8
diff --git a/tools/gn/bootstrap/bootstrap.py b/tools/gn/bootstrap/bootstrap.py
index 8252799..5b71d94 100755
--- a/tools/gn/bootstrap/bootstrap.py
+++ b/tools/gn/bootstrap/bootstrap.py
@@ -524,6 +524,7 @@
       'base/trace_event/memory_dump_session_state.cc',
       'base/trace_event/memory_infra_background_whitelist.cc',
       'base/trace_event/memory_peak_detector.cc',
+      'base/trace_event/memory_tracing_observer.cc',
       'base/trace_event/process_memory_dump.cc',
       'base/trace_event/process_memory_maps.cc',
       'base/trace_event/process_memory_totals.cc',