Intrinsify [] for ExternalUint8 and Uint8 typed data.

tests/standalone/typed_data_test.dart

Index: tests/standalone/typed_data_test.dart
===================================================================
--- tests/standalone/typed_data_test.dart	(revision 36830)
+++ tests/standalone/typed_data_test.dart	(working copy)
@@ -60,6 +60,9 @@
       typed_data[1] = 1.2;
     });
   }
+  Expect.throws(() => typed_data[-1]);
+  Expect.throws(() => typed_data[100]);
+  Expect.throws(() => typed_data[2.0]);
 }
 
 void testUnsignedTypedDataRange(bool check_throws) {
@@ -87,6 +90,9 @@
       typed_data[1] = 1.2;
     });
   }
+  Expect.throws(() => typed_data[-1]);
+  Expect.throws(() => typed_data[100]);
+  Expect.throws(() => typed_data[2.0]);
 }
 
 void testClampedUnsignedTypedDataRangeHelper(Uint8ClampedList typed_data,