Validate use of correct timing instance

Change-Id: Ic30c37154156e183f5ba209fda9c337713272544
diff --git a/src/main/java/com/android/tools/r8/utils/timing/PerfettoThreadTiming.java b/src/main/java/com/android/tools/r8/utils/timing/PerfettoThreadTiming.java
index ef3a805..584f289 100644
--- a/src/main/java/com/android/tools/r8/utils/timing/PerfettoThreadTiming.java
+++ b/src/main/java/com/android/tools/r8/utils/timing/PerfettoThreadTiming.java
@@ -31,6 +31,7 @@
 
   @Override
   public Timing end() {
+    assert threadTrack.getId() == Thread.currentThread().getId();
     threadTrack.endSection();
     depth--;
     return this;
diff --git a/src/main/java/com/android/tools/r8/utils/timing/PerfettoTiming.java b/src/main/java/com/android/tools/r8/utils/timing/PerfettoTiming.java
index 88b52b9..3d8b3fc 100644
--- a/src/main/java/com/android/tools/r8/utils/timing/PerfettoTiming.java
+++ b/src/main/java/com/android/tools/r8/utils/timing/PerfettoTiming.java
@@ -73,6 +73,7 @@
 
   @Override
   public Timing begin(String title) {
+    assert threadTrack.getId() == Thread.currentThread().getId();
     threadTrack.beginSection(title);
     depth++;
     return this;
@@ -80,6 +81,7 @@
 
   @Override
   public Timing end() {
+    assert threadTrack.getId() == Thread.currentThread().getId();
     threadTrack.endSection();
     depth--;
     return this;