Adds a feature to MHTML serialization that omits subframes and subresources marked no-store.

content/renderer/render_frame_impl.cc

Index: content/renderer/render_frame_impl.cc
diff --git a/content/renderer/render_frame_impl.cc b/content/renderer/render_frame_impl.cc
index 4a09e2253c41ddda7c3546282474515d521e3a9e..e89c24e3943c57a922333682d3e222abce637791 100644
--- a/content/renderer/render_frame_impl.cc
+++ b/content/renderer/render_frame_impl.cc
@@ -707,6 +707,13 @@ class MHTMLPartsGenerationDelegate
     return WebString::fromUTF8(content_id);
   }
 
+  blink::WebFrameSerializerCacheControlPolicy cacheControlPolicy() override {
+    return static_cast<blink::WebFrameSerializerCacheControlPolicy>(
+        params_.mhtml_cache_control_policy);
+  }
+
+  bool useBinaryEncoding() override { return params_.mhtml_binary_encoding; }
+
  private:
   const FrameMsg_SerializeAsMHTML_Params& params_;
   std::set<std::string>* digests_of_uris_of_serialized_resources_;
@@ -4948,27 +4955,32 @@ void RenderFrameImpl::OnSerializeAsMHTML(
   DCHECK(!mhtml_boundary.isEmpty());
 
   WebData data;
-  bool success = true;
   std::set<std::string> digests_of_uris_of_serialized_resources;
   MHTMLPartsGenerationDelegate delegate(
       params, &digests_of_uris_of_serialized_resources);
 
+  bool success = true;
+
   // Generate MHTML header if needed.
   if (IsMainFrame()) {
-    blink::WebFrameSerializerCacheControlPolicy policy =
-        static_cast<blink::WebFrameSerializerCacheControlPolicy>(
-            params.mhtml_cache_control_policy);
-    success = WebFrameSerializer::generateMHTMLHeader(mhtml_boundary, policy,
-                                                      GetWebFrame(), &data);
-    if (success && file.WriteAtCurrentPos(data.data(), data.size()) < 0) {
+    // |data| can be empty if the main frame should be skipped.  If the main
+    // frame is
+    // skipped, then the whole archive is bad, so bail to the error condition.
+    WebData data = WebFrameSerializer::generateMHTMLHeader(
+        mhtml_boundary, GetWebFrame(), &delegate);
+    if (data.size() == 0 ||
+        file.WriteAtCurrentPos(data.data(), data.size()) < 0) {
       success = false;
     }
   }
 
-  // Generate MHTML parts.
+  // Generate MHTML parts.  Note that if this is not the main frame, then even
+  // skipping the whole parts generation step is not an error - it simply
+  // results in an omitted resource in the final file.
   if (success) {
-    data = WebFrameSerializer::generateMHTMLParts(
-        mhtml_boundary, GetWebFrame(), params.mhtml_binary_encoding, &delegate);
+    // |data| can be empty if the frame should be skipped, but this is OK.
+    data = WebFrameSerializer::generateMHTMLParts(mhtml_boundary, GetWebFrame(),
+                                                  &delegate);
     // TODO(jcivelli): write the chunks in deferred tasks to give a chance to
     //                 the message loop to process other events.
     if (file.WriteAtCurrentPos(data.data(), data.size()) < 0) {

[Łukasz Anforowicz, 2016/05/19 18:50:17]

I think we also need the |data.size() == 0| check here?  (similarily to how
you've added it to the IsMainFrame case on line 4971).

[dewittj, 2016/05/19 19:44:55]

No, we don't want to fail if any non-main-frame resource is skipped.  We just
want to silently skip it.

The implementation did write 0 bytes to the file, which is probably bad.  So I
updated it to include a size check.

[Łukasz Anforowicz, 2016/05/19 19:51:24]

I see.  We might need to revisit if generating bottom-up and wanting to
distinguish between success/wrote-mhtml and success/skipped-frame.  Looks good
for now.