Use TaskScheduler instead of WorkerPool in v8_platform.cc.

net/proxy/proxy_resolver_v8_tracing_unittest.cc

Index: net/proxy/proxy_resolver_v8_tracing_unittest.cc
diff --git a/net/proxy/proxy_resolver_v8_tracing_unittest.cc b/net/proxy/proxy_resolver_v8_tracing_unittest.cc
index 3456f559d82a3ec7e183d97a78e29c867f2853d8..df3e82d5c9552aae18df9f314a44b990abda816f 100644
--- a/net/proxy/proxy_resolver_v8_tracing_unittest.cc
+++ b/net/proxy/proxy_resolver_v8_tracing_unittest.cc
@@ -13,6 +13,7 @@
 #include "base/run_loop.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/synchronization/waitable_event.h"
+#include "base/test/scoped_async_task_scheduler.h"
 #include "base/threading/platform_thread.h"
 #include "base/threading/thread_checker.h"
 #include "base/values.h"
@@ -949,6 +950,10 @@ TEST_F(ProxyResolverV8TracingTest, Terminate) {
 // this test was written) each ProxyResolverV8Tracing creates its own thread to
 // run V8 on, however each thread is operating on the same v8::Isolate.
 TEST_F(ProxyResolverV8TracingTest, MultipleResolvers) {
+  // Required by gin::V8Platform::CallOnBackgroundThread(). Can't be a
+  // ScopedTaskScheduler because v8 synchronously waits for tasks to run.
+  base::test::ScopedAsyncTaskScheduler scoped_async_task_scheduler;
+
   // ------------------------
   // Setup resolver0
   // ------------------------