Attach UTF8_STRING type data to data offer

The version of GTK3 used in Debian stretch does not use clipboard data
marked as test/plain, but will use UTF8_STRING.

Bug: 793688
Test: Paste from Chrome into gedit
Change-Id: Id1b08e270fd385d287c729fe5594832753b845df
Reviewed-on: https://chromium-review.googlesource.com/1000523
Commit-Queue: Zach Reizner <zachr@chromium.org>
Reviewed-by: David Reveman <reveman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#549074}

components/exo/data_offer.cc

@@ -21,6 +21,7 @@ namespace exo {
 namespace {
 
 constexpr char kTextMimeTypeUtf8[] = "text/plain;charset=utf-8";
+constexpr char kUtf8String[] = "UTF8_STRING";
 constexpr char kUriListSeparator[] = "\r\n";
 
 class RefCountedString16 : public base::RefCountedMemory {
@@ -181,9 +182,12 @@ void DataOffer::SetClipboardData(FileHelper* file_helper,
     base::string16 content;
     data.ReadText(ui::CLIPBOARD_TYPE_COPY_PASTE, &content);
     std::string utf8_content = base::UTF16ToUTF8(content);
-    data_.emplace(std::string(kTextMimeTypeUtf8),
-                  base::RefCountedString::TakeString(&utf8_content));
+    scoped_refptr<base::RefCountedString> utf8_ref =
+        base::RefCountedString::TakeString(&utf8_content);
+    data_.emplace(std::string(kTextMimeTypeUtf8), utf8_ref);
+    data_.emplace(std::string(kUtf8String), utf8_ref);
     delegate_->OnOffer(std::string(kTextMimeTypeUtf8));
+    delegate_->OnOffer(std::string(kUtf8String));
   }
 }
 

components/exo/data_offer_unittest.cc

@@ -359,8 +359,9 @@ TEST_F(DataOfferTest, SetClipboardData) {
   data_offer.SetClipboardData(&file_helper,
                               *ui::Clipboard::GetForCurrentThread());
 
-  EXPECT_EQ(1u, delegate.mime_types().size());
+  EXPECT_EQ(2u, delegate.mime_types().size());
   EXPECT_EQ("text/plain;charset=utf-8", delegate.mime_types()[0]);
+  EXPECT_EQ("UTF8_STRING", delegate.mime_types()[1]);
 
   base::ScopedFD read_pipe;
   base::ScopedFD write_pipe;