encodeUtf8 an image data doesn't work on firefox

[DartBot]

Originally opened as dart-lang/sdk#11527

This issue was originally filed by Thomas.Dela...@gmail.com

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What steps will reproduce the problem?

1. load an image with HttpRequest (mine was 5mb)
2. do an encodeUtf8(request.responseText)
3. see firefox stop the script of dart2js

What is the expected output? What do you see instead?
expected : finish encoding
see instead : script takes too long times to respond

What version of the product are you using? On what operating system?
Dart Editor version 0.5.20_r24160
Dart SDK version 0.5.20.2_r24160
Firefox 21.0
MacBook Pro Retina (2012) OS X 10.8.4

[DartBot]

<img src="https://avatars.githubusercontent.com/u/3276024?v=3" align="left" width="48" height="48"hspace="10"> Comment by anders-sandholm

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Added Area-Library, Library-Utf, Triaged labels.

[DartBot]

<img src="https://avatars.githubusercontent.com/u/4865287?v=3" align="left" width="48" height="48"hspace="10"> Comment by lrhn

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Is the responseText getter meaningful for an image (which sounds like it should be binary data)?
Try setting the responseType to "ArrayBuffer" or "Blob" and get the bytes fusing "response". You shouldn't need to UTF-8 encode anything to get bytes then.
Does this help?

Also, try using UTF8.encode from dart:convert instead of encodeUtf8 from package:utf, and see if it is faster/more compliant.

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Removed Area-Library label.
Added Area-Pkg, NeedsInfo labels.

[DartBot]

<img src="https://avatars.githubusercontent.com/u/3276024?v=3" align="left" width="48" height="48"hspace="10"> Comment by anders-sandholm

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Removed Library-Utf label.
Added Pkg-Utf label.