Improve filtering of files for text search

[pq]

[user feedback]

Text search searches through generated JavaScript files and picture files. Please restrict the search to include relevant files.

[pq]

Currently dart.js and dart.js_ files are ignored and binary files should be ignored based on a quick scan of content (TextSearchExecutor.hasBinaryContent(CharSequence, File)) but this last bit should be verified...

[pq]

Fixed.

http://codereview.chromium.org/10387165/

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Added Fixed label.