perfetto-ui: Show slice details on click

You can now click on a slice and see the details
about it in the panel below.

This is just the logic to display the info, improvements to be made
in future CLs include:
- formatting the info nicely
- unselecting a slice
- showing which slice has been selected in some way
- showing the panel on click

Bug:118893776
Change-Id: Id796149ae5a02105c2eeb436544c2c944df8846b
diff --git a/src/trace_processor/trace_storage.h b/src/trace_processor/trace_storage.h
index 8b5402c..2c64371 100644
--- a/src/trace_processor/trace_storage.h
+++ b/src/trace_processor/trace_storage.h
@@ -54,6 +54,7 @@
   kCounters = 1,
   kRawEvents = 2,
   kInstants = 3,
+  kSched = 4,
 };
 
 // The top 8 bits are set to the TableId and the bottom 32 to the row of the