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

content/browser/web_contents/web_drag_source_mac.mm

Index: content/browser/web_contents/web_drag_source_mac.mm
diff --git a/content/browser/web_contents/web_drag_source_mac.mm b/content/browser/web_contents/web_drag_source_mac.mm
index 2063b093599ecfdf719dc8b25583aba67d0dc94b..336d072febeeb97e147e35ba5a45642f9851bd96 100644
--- a/content/browser/web_contents/web_drag_source_mac.mm
+++ b/content/browser/web_contents/web_drag_source_mac.mm
@@ -343,11 +343,6 @@ void PromiseWriterHelper(const WebDropData& drop_data,
       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())];
@@ -433,6 +428,15 @@ void PromiseWriterHelper(const WebDropData& drop_data,
     }
   }
 
+  // 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]