Add Dart class for _ExternalUint8ClampedArray and API to allocate it.

runtime/include/dart_api.h

Index: runtime/include/dart_api.h
===================================================================
--- runtime/include/dart_api.h	(revision 17018)
+++ runtime/include/dart_api.h	(working copy)
@@ -1672,6 +1672,23 @@
                                                   Dart_PeerFinalizer callback);
 
 /**
+ * Returns a clamped ByteArray which references an external array of
+ * 8-bit bytes.

[siva, 2013/01/15 00:54:23]

Maybe we should also add a line here which explains what a clamped ByteArray is.

[srdjan, 2013/01/15 01:11:10]

Done.

+ *
+ * \param value An array of 8-bit bytes. This array must not move.
+ * \param length The length of the array.
+ * \param peer An external pointer to associate with this byte array.
+ *
+ * \return The ByteArray object if no error occurs. Otherwise returns

[siva, 2013/01/15 00:54:23]

The clamped ByteArray object if

[srdjan, 2013/01/15 01:11:10]

Done.

+ *   an error handle.
+ */
+DART_EXPORT Dart_Handle Dart_NewExternalClampedByteArray(
+    uint8_t* data,
+    intptr_t length,
+    void* peer,
+    Dart_PeerFinalizer callback);
+
+/**
  * Retrieves the data pointer associated with an external ByteArray.
  */
 DART_EXPORT Dart_Handle Dart_ExternalByteArrayGetData(Dart_Handle object,