Add hovering feature to AshDevToolsDOMAgent

ash/common/devtools/ash_devtools_unittest.cc

Index: ash/common/devtools/ash_devtools_unittest.cc
diff --git a/ash/common/devtools/ash_devtools_unittest.cc b/ash/common/devtools/ash_devtools_unittest.cc
index 2bdc8ccc1b1b370fdd64be7ad4f3ac96a6e8c332..e5106cb661051fad2a19408c52c47615e8a1f45a 100644
--- a/ash/common/devtools/ash_devtools_unittest.cc
+++ b/ash/common/devtools/ash_devtools_unittest.cc
@@ -10,6 +10,7 @@
 #include "ash/common/wm_shell.h"
 #include "ash/common/wm_window.h"
 #include "base/strings/stringprintf.h"
+#include "base/threading/thread_task_runner_handle.h"
 #include "ui/views/widget/native_widget_private.h"
 #include "ui/views/widget/widget.h"
 
@@ -140,8 +141,8 @@ class AshDevToolsTest : public AshTest {
     fake_frontend_channel_ = base::MakeUnique<FakeFrontendChannel>();
     uber_dispatcher_ =
         base::MakeUnique<UberDispatcher>(fake_frontend_channel_.get());
-    dom_agent_ =
-        base::MakeUnique<devtools::AshDevToolsDOMAgent>(WmShell::Get());
+    dom_agent_ = base::MakeUnique<devtools::AshDevToolsDOMAgent>(
+        WmShell::Get(), base::ThreadTaskRunnerHandle::Get());
     dom_agent_->Init(uber_dispatcher_.get());
   }