Fixing overrideMimeType on IE10.

sdk/lib/html/dartium/html_dartium.dart

Index: sdk/lib/html/dartium/html_dartium.dart
diff --git a/sdk/lib/html/dartium/html_dartium.dart b/sdk/lib/html/dartium/html_dartium.dart
index 72411293646d15e7faecc87ec3eba50eec181bb1..7cc601d9a4e61c358c2ce694745bdf5f7f7f3bb2 100644
--- a/sdk/lib/html/dartium/html_dartium.dart
+++ b/sdk/lib/html/dartium/html_dartium.dart
@@ -11333,6 +11333,14 @@ class HttpRequest extends EventTarget {
     return true;
   }
 
+  /**
+   * Checks to see if the overrideMimeType method is supported on the current
+   * platform.
+   */
+  static bool get supportsOverrideMimeType {
+    return true;
+  }
+
   HttpRequest.internal() : super.internal();
 
   @DomName('XMLHttpRequest.abortEvent')
@@ -11594,6 +11602,9 @@ class HttpRequest extends EventTarget {
    */
   @DomName('XMLHttpRequest.overrideMimeType')
   @DocsEditable
+  @SupportedBrowser(SupportedBrowser.CHROME)
+  @SupportedBrowser(SupportedBrowser.FIREFOX)
+  @SupportedBrowser(SupportedBrowser.SAFARI)
   void overrideMimeType(String override) native "XMLHttpRequest_overrideMimeType_Callback";
 
   @DomName('XMLHttpRequest.removeEventListener')