Script streaming: more UTF-8 handing fixes (again).

Script streaming: more UTF-8 handing fixes (again).

1) Since we fill the output buffer both from the chunks and the conversion
buffer, it's possible that we run out of space and call CopyCharsHelper with 0
length. The underlying functions don't handle it gracefully, so check there.

2) There was a bug where we used to try to copy too many characters from the
beginning of the data chunk into the conversion buffer. Continuation bytes in
UTF-8 are of the form 0b10XXXXXX. If a byte is bigger than that, it's the first
byte of a new UTF-8 character and we should ignore it.

These two together (or maybe in combination with surrogates) are a probable
reason for crbug.com/420932.

3) The test data was off; \uc481 is \xec\x92\x81.

BUG=420932
LOG=N
R=yangguo@chromium.org

Committed: https://code.google.com/p/v8/source/detail?r=24725

[marja, 2014-10-17 14:14:03]

marja@chromium.org changed reviewers:
+ yangguo@chromium.org

[marja, 2014-10-17 14:14:03]

yangguo@, I unfortunately had to fix the UTF-8 handling once more, PTAL.

[Yang, 2014-10-20 08:29:40]

On 2014/10/17 14:14:03, marja wrote:
> yangguo@, I unfortunately had to fix the UTF-8 handling once more, PTAL.

lgtm.

[marja, 2014-10-20 09:23:53]

Committed patchset #2 (id:20001) manually as 24725 (presubmit successful).