Fix BlockHound false-positive in ConflatedChannel (#2881)

Fixes #2866

Author: qwwdfsad

kotlinx-coroutines-debug/src/CoroutinesBlockHoundIntegration.kt

@@ -135,7 +135,7 @@ public class CoroutinesBlockHoundIntegration : BlockHoundIntegration {
      */
     private fun BlockHound.Builder.allowBlockingCallsInConflatedChannel() {
         for (method in listOf("offerInternal", "offerSelectInternal", "pollInternal", "pollSelectInternal",
-            "onCancelIdempotent"))
+            "onCancelIdempotent", "isEmpty", "enqueueReceiveInternal"))
         {
             allowBlockingCallsInside("kotlinx.coroutines.channels.ConflatedChannel", method)
         }

kotlinx-coroutines-debug/test/BlockHoundTest.kt

@@ -4,6 +4,7 @@ import kotlinx.coroutines.channels.*
 import org.junit.*
 import reactor.blockhound.*
 
+@Suppress("UnusedEquals", "DeferredResultUnused", "BlockingMethodInNonBlockingContext")
 class BlockHoundTest : TestBase() {
 
     @Before
@@ -12,21 +13,21 @@ class BlockHoundTest : TestBase() {
     }
 
     @Test(expected = BlockingOperationError::class)
-    fun shouldDetectBlockingInDefault() = runTest {
+    fun testShouldDetectBlockingInDefault() = runTest {
         withContext(Dispatchers.Default) {
             Thread.sleep(1)
         }
     }
 
     @Test
-    fun shouldNotDetectBlockingInIO() = runTest {
+    fun testShouldNotDetectBlockingInIO() = runTest {
         withContext(Dispatchers.IO) {
             Thread.sleep(1)
         }
     }
 
     @Test
-    fun shouldNotDetectNonblocking() = runTest {
+    fun testShouldNotDetectNonblocking() = runTest {
         withContext(Dispatchers.Default) {
             val a = 1
             val b = 2
@@ -54,7 +55,7 @@ class BlockHoundTest : TestBase() {
     }
 
     @Test
-    fun testChannelsNotBeingConsideredBlocking() = runTest {
+    fun testChannelNotBeingConsideredBlocking() = runTest {
         withContext(Dispatchers.Default) {
             // Copy of kotlinx.coroutines.channels.ArrayChannelTest.testSimple
             val q = Channel<Int>(1)
@@ -74,6 +75,24 @@ class BlockHoundTest : TestBase() {
         }
     }
 
+    @Test
+    fun testConflatedChannelsNotBeingConsideredBlocking() = runTest {
+        withContext(Dispatchers.Default) {
+            val q = Channel<Int>(Channel.CONFLATED)
+            check(q.isEmpty)
+            check(!q.isClosedForReceive)
+            check(!q.isClosedForSend)
+            val sender = launch {
+                q.send(1)
+            }
+            val receiver = launch {
+                q.receive() == 1
+            }
+            sender.join()
+            receiver.join()
+        }
+    }
+
     @Test(expected = BlockingOperationError::class)
     fun testReusingThreadsFailure() = runTest {
         val n = 100