Interactions with TreeObserverManager moved to main thread

Summary: Needed for next diff

Reviewed By: lblasa

Differential Revision: D42453228

fbshipit-source-id: 29e2655bf08376cd12a98ab61fe95b804b0c7ba1

android/src/main/java/com/facebook/flipper/plugins/uidebugger/UIDebuggerFlipperPlugin.kt

@@ -18,6 +18,9 @@ import com.facebook.flipper.plugins.uidebugger.descriptors.MetadataRegister
 import com.facebook.flipper.plugins.uidebugger.model.InitEvent
 import com.facebook.flipper.plugins.uidebugger.model.MetadataUpdateEvent
 import com.facebook.flipper.plugins.uidebugger.observers.TreeObserverFactory
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.launch
 import kotlinx.serialization.json.Json
 
 const val LogTag = "ui-debugger"
@@ -28,6 +31,7 @@ class UIDebuggerFlipperPlugin(
     observerFactory: TreeObserverFactory?
 ) : FlipperPlugin {
 
+  val mainScope = CoroutineScope(Dispatchers.Main)
   private val context: Context =
       Context(
           ApplicationRef(application),
@@ -61,7 +65,7 @@ class UIDebuggerFlipperPlugin(
             MetadataUpdateEvent.serializer(),
             MetadataUpdateEvent(MetadataRegister.extractPendingMetadata())))
 
-    context.treeObserverManager.start()
+    mainScope.launch { context.treeObserverManager.start() }
   }
 
   @Throws(Exception::class)
@@ -71,8 +75,10 @@ class UIDebuggerFlipperPlugin(
 
     MetadataRegister.reset()
 
-    context.treeObserverManager.stop()
-    context.bitmapPool.recycleAll()
+    mainScope.launch {
+      context.treeObserverManager.stop()
+      context.bitmapPool.recycleAll()
+    }
   }
 
   override fun runInBackground(): Boolean {