clovis: Add a method to slim a trace by dropping large objects.

tools/android/loading/loading_trace.py

Index: tools/android/loading/loading_trace.py
diff --git a/tools/android/loading/loading_trace.py b/tools/android/loading/loading_trace.py
index 6dbd13deb9f12075a812f2f1a7fc97b5e7238673..7630bcc07cff699482928a6eb80a2e00d6e5d88f 100644
--- a/tools/android/loading/loading_trace.py
+++ b/tools/android/loading/loading_trace.py
@@ -34,7 +34,8 @@ class LoadingTrace(object):
     self.metadata = metadata
     self.page_track = page
     self.request_track = request
-    self.tracing_track = tracing_track
+    self._tracing_track = tracing_track
+    self._tracing_json_str = None
 
   def ToJsonDict(self):
     """Returns a dictionary representing this instance."""
@@ -94,3 +95,23 @@ class LoadingTrace(object):
                     else categories))
     connection.MonitorUrl(url, timeout_seconds=timeout_seconds)
     return cls(url, chrome_metadata, page, request, trace)
+
+  @property
+  def tracing_track(self):
+    if not self._tracing_track:
+      self._RestoreTracingTrack()
+    return self._tracing_track
+
+  def Slim(self):
+    """Slims the memory usage of a trace by dropping the TraceEvents from it.
+
+    The tracing track is restored on-demand when accessed.
+    """
+    self._tracing_json_str = json.dumps(self._tracing_track.ToJsonDict())
+    self._tracing_track = None
+
+  def _RestoreTracingTrack(self):
+    assert self._tracing_json_str
+    self._tracing_track = tracing.TracingTrack.FromJsonDict(
+        json.loads(self._tracing_json_str))
+    self._tracing_json_str = None