processor: Parse TrackEvent track associations

Adds support for parsing TrackDescriptors and TrackEvent's track_uuid
field which were added in aosp/1101291.

Bug: 130786981
Change-Id: I2c14b6dc0407adb6b53c30fd8cc5524f7b0b6515
diff --git a/src/trace_processor/trace_storage.h b/src/trace_processor/trace_storage.h
index 0799eae..b34e483 100644
--- a/src/trace_processor/trace_storage.h
+++ b/src/trace_processor/trace_storage.h
@@ -1147,7 +1147,8 @@
     return unique_processes_[upid];
   }
 
-  const Thread& GetThread(UniqueTid utid) const {
+  // Virtual for testing.
+  virtual const Thread& GetThread(UniqueTid utid) const {
     // Allow utid == 0 for idle thread retrieval.
     PERFETTO_DCHECK(utid < unique_threads_.size());
     return unique_threads_[utid];