Only lower-case ContentType's values if the name is 'charset'.

sdk/lib/io/http.dart

Index: sdk/lib/io/http.dart
diff --git a/sdk/lib/io/http.dart b/sdk/lib/io/http.dart
index d908338bc7a0ebc8776b3d93f4377b13b46f04eb..1824a80c4f4e348bb265eceef442ae42a2899617 100644
--- a/sdk/lib/io/http.dart
+++ b/sdk/lib/io/http.dart
@@ -750,8 +750,9 @@ abstract class ContentType implements HeaderValue {
    * sub type. The charset and additional parameters can also be set
    * using [charset] and [parameters]. If charset is passed and
    * [parameters] contains charset as well the passed [charset] will
-   * override the value in parameters. Keys and values passed in
-   * parameters will be converted to lower case.
+   * override the value in parameters. Keys passed in parameters will be
+   * converted to lower case. Values passed in parameters will be
+   * converted to lower case, only if the parameter name is 'charset'.

[Lasse Reichstein Nielsen, 2014/11/03 10:51:17]

Change last sentence to:
"The `charset` entry, whether passed as `charset` or in `parameters`, will have
its value converted to lower-case."

Talking about "Values ... will be converted ... only if (single case)" makes the
plurality of "Values" sound odd.

[Anders Johnsen, 2014/11/03 12:38:29]

Done.

    */
   factory ContentType(String primaryType,
                       String subType,