[Offline Pages] Adding missing image/CSS detection in FrameSerializer.

third_party/WebKit/Source/web/tests/WebFrameSerializerSanitizationTest.cpp

Index: third_party/WebKit/Source/web/tests/WebFrameSerializerSanitizationTest.cpp
diff --git a/third_party/WebKit/Source/web/tests/WebFrameSerializerSanitizationTest.cpp b/third_party/WebKit/Source/web/tests/WebFrameSerializerSanitizationTest.cpp
index 1fecdcde433557145b04d435637f7b4184385492..f0136b43021a915fe2da9b6ea937aa29cdfb55c7 100644
--- a/third_party/WebKit/Source/web/tests/WebFrameSerializerSanitizationTest.cpp
+++ b/third_party/WebKit/Source/web/tests/WebFrameSerializerSanitizationTest.cpp
@@ -70,6 +70,7 @@ class SimpleMHTMLPartsGenerationDelegate
 
   bool UseBinaryEncoding() final { return false; }
   bool RemovePopupOverlay() final { return remove_popup_overlay_; }
+  bool UsePageProblemDetectors() final { return false; }
 
   bool remove_popup_overlay_;
 };