Update libxml to 2.7.7.

third_party/libxml/patches/libxml-disable-autodetect

+See comment below inline in the patch.
+It'd be nice to fix this properly but that will require upstream WebKit
+changes; for now, we can just patch out some code to keep behavior as it
+was before.
+
+diff --git a/third_party/libxml/parser.c b/third_party/libxml/parser.c
+index 3ba2a06..4a3cde5 100644
+--- a/third_party/libxml/parser.c
++++ b/third_party/libxml/parser.c
+@@ -11545,6 +11545,20 @@ xmldecl_done:
+        int cur = ctxt->input->cur - ctxt->input->base;
+        int res;
+ 
++        /* Chromium note: commenting out the following block of code is a gory
++         * hack, meant to partially undo
++         *  http://git.gnome.org/browse/libxml2/commit/?id=a6c76a
++         *
++         * WebKit and libxml disagree about who is responsible for the
++         * document encoding.
++         *
++         * This bug:
++         *   https://bugs.webkit.org/show_bug.cgi?id=30508
++         * has links to test cases, libxml bug reports, and mailing list threads
++         * arguing about it; for now, though, we can just undo the change that
++         * caused libxml to regress.
++         */
++#if 0
+         /*
+          * Specific handling if we autodetected an encoding, we should not
+          * push more than the first line ... which depend on the encoding
+@@ -11580,6 +11594,7 @@ xmldecl_done:
+                 remain = 0;
+             }
+         }
++#endif
+        res =xmlParserInputBufferPush(ctxt->input->buf, size, chunk);
+        if (res < 0) {
+            ctxt->errNo = XML_PARSER_EOF;