Provide default implementation of QuicheThread.

This uses STL thread class, which is not allowed inside google3 or Chromium (since those have their own thread abstractions), but is the best we can get in an open-source project otherwise.

PiperOrigin-RevId: 449014471
diff --git a/build/source_list.bzl b/build/source_list.bzl
index 59d5cd7..2a2bb10 100644
--- a/build/source_list.bzl
+++ b/build/source_list.bzl
@@ -1400,6 +1400,7 @@
 ]
 default_platform_impl_test_support_hdrs = [
     "common/platform/default/quiche_platform_impl/quiche_test_loopback_impl.h",
+    "common/platform/default/quiche_platform_impl/quiche_thread_impl.h",
 ]
 default_platform_impl_test_support_srcs = [
     "common/platform/default/quiche_platform_impl/quiche_test_loopback_impl.cc",
diff --git a/build/source_list.gni b/build/source_list.gni
index 0246d0d..9f1ee66 100644
--- a/build/source_list.gni
+++ b/build/source_list.gni
@@ -1400,6 +1400,7 @@
 ]
 default_platform_impl_test_support_hdrs = [
     "src/quiche/common/platform/default/quiche_platform_impl/quiche_test_loopback_impl.h",
+    "src/quiche/common/platform/default/quiche_platform_impl/quiche_thread_impl.h",
 ]
 default_platform_impl_test_support_srcs = [
     "src/quiche/common/platform/default/quiche_platform_impl/quiche_test_loopback_impl.cc",
diff --git a/build/source_list.json b/build/source_list.json
index 9df338c..72b7055 100644
--- a/build/source_list.json
+++ b/build/source_list.json
@@ -1398,7 +1398,8 @@
     "quiche/common/platform/default/quiche_platform_impl/quiche_file_utils_impl.cc"
   ],
   "default_platform_impl_test_support_hdrs": [
-    "quiche/common/platform/default/quiche_platform_impl/quiche_test_loopback_impl.h"
+    "quiche/common/platform/default/quiche_platform_impl/quiche_test_loopback_impl.h",
+    "quiche/common/platform/default/quiche_platform_impl/quiche_thread_impl.h"
   ],
   "default_platform_impl_test_support_srcs": [
     "quiche/common/platform/default/quiche_platform_impl/quiche_test_loopback_impl.cc"