Optimize length access on all JSIndexable things.

sdk/lib/_internal/compiler/implementation/ssa/codegen.dart

Index: sdk/lib/_internal/compiler/implementation/ssa/codegen.dart
diff --git a/sdk/lib/_internal/compiler/implementation/ssa/codegen.dart b/sdk/lib/_internal/compiler/implementation/ssa/codegen.dart
index fa4d2e1efa24441acc99e73836dfab37dac95449..ea12db454189b7407bfb096845d655b0d3a7c3ba 100644
--- a/sdk/lib/_internal/compiler/implementation/ssa/codegen.dart
+++ b/sdk/lib/_internal/compiler/implementation/ssa/codegen.dart
@@ -1648,7 +1648,7 @@ abstract class SsaCodeGenerator implements HVisitor, HBlockInformationVisitor {
   visitFieldGet(HFieldGet node) {
     use(node.receiver);
     Element element = node.element;
-    if (element == backend.jsArrayLength || element == backend.jsStringLength) {
+    if (element == backend.jsIndexableLength) {
       // We're accessing a native JavaScript property called 'length'
       // on a JS String or a JS array. Therefore, the name of that
       // property should not be mangled.