More optimization of _uriEncode.

More optimization of _uriEncode.

Avoid doing the encoding of the original string for ASCII/LATIN1/UTF-8.
For mostly ASCII strings, the encoding is just a copying overhead.

[sra1, 2015-11-03 17:28:42]

sra@google.com changed reviewers:
+ sra@google.com

[sra1, 2015-11-03 17:28:42]

I can't patch and run this.

I suspect that the extra code will make the code size cost of  Uri even higher,
so I don't think this is a good avenue to continue, at least for dart2js.

If you think this is valuable on the VM then we need to have a VM/dart2js patch
split, and push the encoding higher so that the dart2js patch can use the
browser's functions.

Why do we allow encodings other than UTF8?

https://codereview.chromium.org/1409053007/diff/20001/sdk/lib/core/uri.dart
File sdk/lib/core/uri.dart (right):

https://codereview.chromium.org/1409053007/diff/20001/sdk/lib/core/uri.dart#n...
sdk/lib/core/uri.dart:1994: const int spaceToPlus = true;
checked mode error

https://codereview.chromium.org/1409053007/diff/20001/sdk/lib/core/uri.dart#n...
sdk/lib/core/uri.dart:2298: result[j] = text.codeUnitAt(j);
StringBuffer does not have []=.

[Lasse Reichstein Nielsen, 2015-11-03 18:04:08]

https://codereview.chromium.org/1409053007/diff/20001/sdk/lib/core/uri.dart
File sdk/lib/core/uri.dart (right):

https://codereview.chromium.org/1409053007/diff/20001/sdk/lib/core/uri.dart#n...
sdk/lib/core/uri.dart:2298: result[j] = text.codeUnitAt(j);
Duh, should be writeCharCode. 
Obviously needs more tests.