dart2js ssa: Open coding of removeLast should use -1 as index

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

Index: pkg/compiler/lib/src/ssa/optimize.dart
diff --git a/pkg/compiler/lib/src/ssa/optimize.dart b/pkg/compiler/lib/src/ssa/optimize.dart
index 977900c2242fe466ffe89008300ffc8f52f6ba37..795b510fbc31ae0b60e76390e1eb499b5c97612b 100644
--- a/pkg/compiler/lib/src/ssa/optimize.dart
+++ b/pkg/compiler/lib/src/ssa/optimize.dart
@@ -1029,8 +1029,13 @@ class SsaCheckInserter extends HBaseVisitor implements OptimizationPhase {
     if (node.isInterceptedCall) return;
     if (element != backend.jsArrayRemoveLast) return;
     if (boundsChecked.contains(node)) return;
-    insertBoundsCheck(
+    // `0` is the index we want to check, but we want to report `-1`, as if we
+    // executed `a[a.length-1]`
+    HBoundsCheck check = insertBoundsCheck(
         node, node.receiver, graph.addConstantInt(0, backend.compiler));
+    HInstruction minusOne = graph.addConstantInt(-1, backend.compiler);
+    check.inputs.add(minusOne);
+    minusOne.usedBy.add(check);
   }
 }