Set encoding to UTF-8 for HTML Imports if no encoding is specified in the HTTP response

LayoutTests/fast/html/imports/encoding-expected.txt

Index: LayoutTests/fast/html/imports/encoding-expected.txt
diff --git a/LayoutTests/fast/html/imports/encoding-expected.txt b/LayoutTests/fast/html/imports/encoding-expected.txt
new file mode 100644
index 0000000000000000000000000000000000000000..c513e92fa82f848c68b8b762909fdfb17e560efc
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+++ b/LayoutTests/fast/html/imports/encoding-expected.txt
@@ -0,0 +1,13 @@
+Test that UTF-8 decoding is applied appropriately to imports
+
+On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".
+
+
+Default encoding should be UTF-8...
+PASS links[0].import.characterSet is "UTF-8"
+And a meta tag should not override it...
+PASS links[1].import.characterSet is "UTF-8"
+PASS successfullyParsed is true
+
+TEST COMPLETE
+