Add support for CSS unicod encoding to the text codec.

chrome/browser/download/save_page_browsertest.cc

Index: chrome/browser/download/save_page_browsertest.cc
diff --git a/chrome/browser/download/save_page_browsertest.cc b/chrome/browser/download/save_page_browsertest.cc
index 0c497e9d93967e1cbcad7abedddfb9b4ce26ab69..f25a5a5624031f72633d5087d0dade55624292c1 100644
--- a/chrome/browser/download/save_page_browsertest.cc
+++ b/chrome/browser/download/save_page_browsertest.cc
@@ -735,6 +735,11 @@ IN_PROC_BROWSER_TEST_F(SavePageAsMHTMLBrowserTest, SavePageAsMHTML) {
   int64_t actual_file_size = -1;
   EXPECT_TRUE(base::GetFileSize(full_file_name, &actual_file_size));
   EXPECT_LE(kFileSizeMin, actual_file_size);
+
+  std::string contents;
+  EXPECT_TRUE(base::ReadFileToString(full_file_name, &contents));
+  // Test for a CSS encoded character.  This used to use HTML encoding.
+  EXPECT_THAT(contents, HasSubstr("content: \"\\e003 \\e004 b\""));
 }
 
 IN_PROC_BROWSER_TEST_F(SavePageBrowserTest, SavePageBrowserTest_NonMHTML) {