Mac: add encoding meta-tag to HTML provided with NSHTMLPboardType.
Mac: add encoding meta-tag to HTML provided with NSHTMLPboardType.

Otherwise, US-ASCII is assumed.

BUG=42661
TEST=dragging text from, e.g., Chinese-language web sites into TextEdit works

Review URL: http://codereview.chromium.org/1820001

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@46029 0039d316-1c4b-4281-b951-d872f2087c98

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