Avoid adding placeholder when deleting last text in root

LayoutTests/editing/pasteboard/copy-paste-content-starting-and-ending-canvas-expected.txt

Index: LayoutTests/editing/pasteboard/copy-paste-content-starting-and-ending-canvas-expected.txt
diff --git a/LayoutTests/editing/pasteboard/copy-paste-content-starting-and-ending-canvas-expected.txt b/LayoutTests/editing/pasteboard/copy-paste-content-starting-and-ending-canvas-expected.txt
new file mode 100644
index 0000000000000000000000000000000000000000..a675105c0516b42c5218858ce9cca09d4dff5877
--- /dev/null
+++ b/LayoutTests/editing/pasteboard/copy-paste-content-starting-and-ending-canvas-expected.txt
@@ -0,0 +1,46 @@
+This tests selecting all, copying, and pasting a content that starts and ends with canvas elements.
+To manually test, copy and paste the content below:
+
+Before paste:
+| "
+"
+| <canvas>
+|   height="100"
+|   style="border: 1px solid black"
+|   width="100"
+| "
+some text
+"
+| <canvas>
+|   height="100"
+|   style="border: 1px solid black"
+|   width="100"
+| "
+some more text
+"
+| <canvas>
+|   height="100"
+|   style="border: 1px solid black"
+|   width="100"
+| "
+"
+
+After paste:
+| <canvas>
+|   height="100"
+|   style="border: 1px solid black;"
+|   width="100"
+| " "
+| "some text"
+| " "
+| <canvas>
+|   height="100"
+|   style="border: 1px solid black;"
+|   width="100"
+| " "
+| "some more text"
+| " "
+| <canvas>
+|   height="100"
+|   style="border: 1px solid black;"
+|   width="100"