dart2js-kernel: associate more compound assignment inner nodes

pkg/compiler/lib/src/ssa/kernel_ast_adapter.dart

Index: pkg/compiler/lib/src/ssa/kernel_ast_adapter.dart
diff --git a/pkg/compiler/lib/src/ssa/kernel_ast_adapter.dart b/pkg/compiler/lib/src/ssa/kernel_ast_adapter.dart
index 1343be0b2db2003b3c9b5bd14a5f6ce701885117..1952e26136c88814e616400b818dee3b8c5cb2e3 100644
--- a/pkg/compiler/lib/src/ssa/kernel_ast_adapter.dart
+++ b/pkg/compiler/lib/src/ssa/kernel_ast_adapter.dart
@@ -198,11 +198,14 @@ class KernelAstAdapter {
     return new Selector.setter(name);
   }
 
-  TypeMask typeOfInvocation(ir.Expression send) {
+  TypeMask typeOfInvocation(ir.MethodInvocation send) {
     ast.Node operatorNode = kernel.nodeToAstOperator[send];
     if (operatorNode != null) {
       return _resultOf(_target).typeOfOperator(operatorNode);
     }
+    if (send.name.name == '[]=') {
+      return _compiler.closedWorld.commonMasks.dynamicType;
+    }
     return _resultOf(_target).typeOfSend(getNode(send));
   }