Don't put HTML onto the clipboard if there is file content data.

content/browser/web_contents/web_drag_source_mac.mm

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #import "content/browser/web_contents/web_drag_source_mac.h"
 
 #include <sys/param.h>
 
 #include "base/bind.h"
 #include "base/file_path.h"
@@ skipping 325 matching lines @@
 
 @implementation WebDragSource (Private)
 
 - (void)fillPasteboard {
   DCHECK(pasteboard_.get());
 
   [pasteboard_
       declareTypes:[NSArray arrayWithObject:ui::kChromeDragDummyPboardType]
              owner:contentsView_];
 
-  // HTML.
-  if (!dropData_->html.string().empty())
-    [pasteboard_ addTypes:[NSArray arrayWithObject:NSHTMLPboardType]
-                    owner:contentsView_];
-
   // URL (and title).
   if (dropData_->url.is_valid()) {
     NSURL* url = [NSURL URLWithString:SysUTF8ToNSString(dropData_->url.spec())];
     // If NSURL creation failed, check for a badly-escaped JavaScript URL.
     // Strip out any existing escapes and then re-escape uniformly.
     if (!url && dropData_->url.SchemeIs(chrome::kJavaScriptScheme)) {
       net::UnescapeRule::Type unescapeRules =
           net::UnescapeRule::SPACES |
           net::UnescapeRule::URL_SPECIAL_CHARS |
           net::UnescapeRule::CONTROL_CHARS;
@@ skipping 65 matching lines @@
       [pasteboard_ setPropertyList:@[SysUTF8ToNSString(fileExtension.substr(1))]
                            forType:NSFilesPromisePboardType];
 
       if (!dropData_->file_contents.empty()) {
         NSArray* types = @[base::mac::CFToNSCast(fileUTI_.get())];
         [pasteboard_ addTypes:types owner:contentsView_];
       }
     }
   }
 
+  // HTML.
+  // Mail.app and TextEdit don't accept drops with both HTML and file content on
+  // them <http://crbug.com/55879>. If there is both file content and HTML in
+  // |dropData_| (as in the case of dragging an image), only provide the file
+  // data.

[Nico, 2012/12/23 00:08:26]

How does the HTML content for just an image look? Can we sniff for that and drop
html in just that case?

(Not sure if it's worth it.)

+  if (!dropData_->html.string().empty() && dropData_->file_contents.empty())
+    [pasteboard_ addTypes:[NSArray arrayWithObject:NSHTMLPboardType]
+                    owner:contentsView_];
+
   // Plain text.
   if (!dropData_->text.string().empty())
     [pasteboard_ addTypes:[NSArray arrayWithObject:NSStringPboardType]
                     owner:contentsView_];
 
   if (!dropData_->custom_data.empty()) {
     [pasteboard_
         addTypes:[NSArray arrayWithObject:ui::kWebCustomDataPboardType]
            owner:contentsView_];
   }
 }
 
 - (NSImage*)dragImage {
   if (dragImage_)
     return dragImage_;
 
   // Default to returning a generic image.
   return content::GetContentClient()->GetNativeImageNamed(
       IDR_DEFAULT_FAVICON).ToNSImage();
 }
 
 @end  // @implementation WebDragSource (Private)