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..29eb8d71a42dbba6ccce531a84559a4758bb57de 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 +4955,35 @@ 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 should_serialize_frame =
+      WebFrameSerializer::frameShouldBeSerializedAsMHTML(GetWebFrame(),
+                                                         &delegate);
+  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) {
+    if (should_serialize_frame) {
+      WebData data = WebFrameSerializer::generateMHTMLHeader(
+          mhtml_boundary, GetWebFrame(), &delegate);
+      if (file.WriteAtCurrentPos(data.data(), data.size()) < 0) {
+        success = false;
+      }
+    } else {
+      // If we can't serialize the main frame, the whole archive is bad.
       success = false;
     }
   }
 
-  // Generate MHTML parts.
-  if (success) {
-    data = WebFrameSerializer::generateMHTMLParts(
-        mhtml_boundary, GetWebFrame(), params.mhtml_binary_encoding, &delegate);
+  // 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 && should_serialize_frame) {
+    data = WebFrameSerializer::generateMHTMLParts(mhtml_boundary, GetWebFrame(),
+                                                  &delegate);

[Łukasz Anforowicz, 2016/05/18 17:27:25]

This skips generating the MHTML part for a subframe, but the parent frame will
continue emitting cid: URIs referring to the subframe (i.e. the subframe will
still be covered by the map in
MHTMLGenerationManager::Job::frame_tree_node_to_content_id_ and therefore will
be used by the parent frame when generating the parent frame's MHTML).

As I wrote in https://crbug.com/570353#c7, I hope that bottom-up generation in
MHTMLGenerationManager::Job can help here (right not MHTML is generated in the
order used by web_contents->ForEachFrame -
https://code.google.com/p/chromium/codesearch#chromium/src/content/browser/do...).

[dewittj, 2016/05/19 04:13:17]

I'd prefer to leave this as-is and address generation order in a subsequent
patch.  Are you okay with that?

[Łukasz Anforowicz, 2016/05/19 17:00:13]

I am fine with that (given that MHTML saved by end-users should not be affected
by the no-store changes and you've checked that Android is gracefully handling
dangling CID URIs).

I assume that you are committing to working on this and landing a fix for the
next milestone (M-53)? :-)

BTW: I am not particularly attached to bottom-up generation option of fixing
this, but I do think that we need to do *something* about the CID behavior - it 
currently results in rather terrible experience for the desktop users who happen
to hit it.

[dewittj, 2016/05/19 18:18:35]

I am going to work on this :)  Perhaps we can agree to work together!

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

Sure - I'll be happy to help :-)

     // 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) {