MHTML generation: safely serialize image documents

third_party/WebKit/Source/web/WebFrameSerializer.cpp

Index: third_party/WebKit/Source/web/WebFrameSerializer.cpp
diff --git a/third_party/WebKit/Source/web/WebFrameSerializer.cpp b/third_party/WebKit/Source/web/WebFrameSerializer.cpp
index 5fdf086b987a4235d190e22fae7cf7de62f0db1f..8d600dda9a1a94d696f37717c9d7cdf5c066d07f 100644
--- a/third_party/WebKit/Source/web/WebFrameSerializer.cpp
+++ b/third_party/WebKit/Source/web/WebFrameSerializer.cpp
@@ -294,6 +294,11 @@ WebThreadSafeData WebFrameSerializer::generateMHTMLParts(
     FrameSerializer serializer(resources, coreDelegate);
     serializer.serializeFrame(*frame);
   }
+
+  // There was an error serializing the frame (e.g. of an image resource).
+  if (resources.isEmpty())
+    return WebThreadSafeData();

[carlosk, 2017/01/06 23:26:36]

To keep tracing logic consistent this should be moved after the TRACE_EVENT_END1
below.

[Charlie Harrison, 2017/01/07 02:31:25]

Good catch, will fix this in a follow up.

+
   TRACE_EVENT_END1("page-serialization",
                    "WebFrameSerializer::generateMHTMLParts serializing",
                    "resource count",
@@ -302,7 +307,6 @@ WebThreadSafeData WebFrameSerializer::generateMHTMLParts(
   // Encode serialized resources as MHTML.
   RefPtr<RawData> output = RawData::create();
   {
-    DCHECK(!resources.isEmpty());
     SCOPED_BLINK_UMA_HISTOGRAM_TIMER(
         "PageSerialization.MhtmlGeneration.EncodingTime.SingleFrame");
     // Frame is the 1st resource (see FrameSerializer::serializeFrame doc