Fix image_decoder unit tests

services/image_decoder/image_decoder_impl_unittest.cc

Index: services/image_decoder/image_decoder_impl_unittest.cc
diff --git a/services/image_decoder/image_decoder_impl_unittest.cc b/services/image_decoder/image_decoder_impl_unittest.cc
index 82c7a0021d00162dc68961e1511e415acf33af40..a04f21d30926a16cab5b033972daa29fc48ec973 100644
--- a/services/image_decoder/image_decoder_impl_unittest.cc
+++ b/services/image_decoder/image_decoder_impl_unittest.cc
@@ -81,6 +81,8 @@ class BlinkInitializer : public blink::Platform {
 
   ~BlinkInitializer() override {}
 
+  blink::WebThread* currentThread() override { return main_thread_.get(); }
+
  private:
   std::unique_ptr<blink::scheduler::WebThreadImplForUtilityThread> main_thread_;