Don't copy hidden selections

Chrome sometimes hides selections*. CTRL+C should not copy
such selections because users expect that CTRL+C has no
effect when their browser doesn't display a selection.

What about cut and paste?
Cut and paste are read/write-operations so they only operate
on _focused_ selections. A focused selection is always visible:

  bool FrameSelection::IsHidden() const {
    if (SelectionHasFocus())
      return false;
    ...

=> Cut and paste already follow the principle of visibility
so we only need to fix "copy". This CL does that.

* See the explainer in crrev.com/525029 for more information.

Bug: 813416
Change-Id: Ibb5f3868e7a5fc37c7522bb753a41ae9568d98e2
Reviewed-on: https://chromium-review.googlesource.com/924027
Commit-Queue: Hugo Holgersson <hugoh@vewd.com>
Reviewed-by: Xiaocheng Hu <xiaochengh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#537633}

third_party/WebKit/Source/core/editing/Editor.cpp

@@ -950,6 +950,12 @@ void Editor::Copy(EditorCommandSource source) {
   if (!CanCopy())
     return;
 
+  // Since copy is a read-only operation it succeeds anytime a selection
+  // is *visible*. In contrast to cut or paste, the selection does not
+  // need to be focused - being visible is enough.
+  if (source == kCommandFromMenuOrKeyBinding && GetFrameSelection().IsHidden())
+    return;
+
   // TODO(editing-dev): The use of UpdateStyleAndLayoutIgnorePendingStylesheets
   // needs to be audited.  See http://crbug.com/590369 for more details.
   // A 'copy' event handler might have dirtied the layout so we need to update

third_party/WebKit/Source/core/editing/EditorTest.cpp

@@ -4,6 +4,7 @@
 
 #include "core/editing/Editor.h"
 
+#include "core/clipboard/Pasteboard.h"
 #include "core/editing/testing/EditingTestBase.h"
 #include "core/html/forms/HTMLInputElement.h"
 
@@ -34,4 +35,25 @@ TEST_F(EditorTest, copyGeneratedPassword) {
   EXPECT_TRUE(editor.CanCopy());
 }
 
+TEST_F(EditorTest, DontCopyHiddenSelections) {
+  const char* body_content =
+      "<input type=checkbox id=checkbox>"
+      "<input id=hiding value=HEY></input>";
+  SetBodyContent(body_content);
+
+  HTMLInputElement& text_control =
+      ToHTMLInputElement(*GetDocument().getElementById("hiding"));
+  text_control.select();
+
+  HTMLInputElement& checkbox =
+      ToHTMLInputElement(*GetDocument().getElementById("checkbox"));
+  checkbox.focus();
+
+  Editor& editor = GetDocument().GetFrame()->GetEditor();
+  editor.Copy(kCommandFromMenuOrKeyBinding);
+
+  const String copied = Pasteboard::GeneralPasteboard()->PlainText();
+  EXPECT_TRUE(copied.IsEmpty()) << copied << " was copied.";
+}
+
 }  // namespace blink