Only inject content scripts into HTML documents. Previously we would inject into SVG and raw XML documents as well.
Only inject content scripts into HTML documents. Previously we would inject into SVG and raw XML documents as well.

Injecting into SVG could conceivably be a feature, but I expect it would count as a "bug" more often than that, so I'm starting conservative.

BUG=39845

Review URL: http://codereview.chromium.org/2389004

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@48693 0039d316-1c4b-4281-b951-d872f2087c98

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