tools/gn: Fix for bootstrap.py to keep it working.

It was missing a trace_event source file to keep things compiling.

BUG=None
TEST=./tools/gn/bootstrap/bootstrap.py
TBR=brettw@chromium.org

Review URL: https://codereview.chromium.org/1376133002

Cr-Original-Commit-Position: refs/heads/master@{#351491}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 38275d22a667c2da73c35ab3cd2b8c26f86c9411

tools/gn/bootstrap/bootstrap.py

diff --git a/tools/gn/bootstrap/bootstrap.py b/tools/gn/bootstrap/bootstrap.py
index cb5e0ab..8764f0d 100755
--- a/tools/gn/bootstrap/bootstrap.py
+++ b/tools/gn/bootstrap/bootstrap.py
@@ -247,6 +247,7 @@
       'base/trace_event/memory_dump_manager.cc',
       'base/trace_event/memory_dump_request_args.cc',
       'base/trace_event/memory_dump_session_state.cc',
+      'base/trace_event/memory_profiler_allocation_context.cc',
       'base/trace_event/process_memory_dump.cc',
       'base/trace_event/process_memory_maps.cc',
       'base/trace_event/process_memory_maps_dump_provider.cc',