Provide dummy Android UI thread with looper for C++ unit tests

base/test/BUILD.gn

Index: base/test/BUILD.gn
diff --git a/base/test/BUILD.gn b/base/test/BUILD.gn
index 91456db0edca1cf1b112463f7aaf3e5356b52498..d2d7c54a88852d8f00a8412ebe4f017bdbdf719d 100644
--- a/base/test/BUILD.gn
+++ b/base/test/BUILD.gn
@@ -112,6 +112,8 @@ source_set("test_support") {
     "test_support_android.h",
     "test_support_ios.h",
     "test_support_ios.mm",
+    "test_ui_thread_android.cc",
+    "test_ui_thread_android.h",
     "thread_test_helper.cc",
     "thread_test_helper.h",
     "trace_event_analyzer.cc",
@@ -203,6 +205,7 @@ if (is_android) {
   generate_jni("base_unittests_jni_headers") {
     sources = [
       "android/java/src/org/chromium/base/ContentUriTestUtils.java",
+      "android/java/src/org/chromium/base/TestUiThread.java",
     ]
     jni_package = "base"
   }