Implement UXTB and UXTH in the ARM integerated assembler.

src/DartARM32/assembler_arm.h

Index: src/DartARM32/assembler_arm.h
diff --git a/src/DartARM32/assembler_arm.h b/src/DartARM32/assembler_arm.h
index dbc1873fef73df35322ce92cd35b62d08d17c897..c85109e3457d52aebb86713cd5db40bc3d8b6d9b 100644
--- a/src/DartARM32/assembler_arm.h
+++ b/src/DartARM32/assembler_arm.h
@@ -1301,6 +1301,12 @@ class Assembler : public ValueObject {
                      Register new_value,
                      FieldContent old_content);
 
+#if 0
+  // Added the following missing operations:
+  //
+  // ARM32::AssemblerARM::uxt() (uxtb and uxth).
+#endif
+
   DISALLOW_ALLOCATION();
   DISALLOW_COPY_AND_ASSIGN(Assembler);
 };