Elide unnecessary context reload in generated stubs.

src/arm/lithium-arm.cc

Index: src/arm/lithium-arm.cc
diff --git a/src/arm/lithium-arm.cc b/src/arm/lithium-arm.cc
index f44ca98aad059da26ffb7bfeb6aa320d9247e5ca..fd55e2460fcbfa2242057be35b096dabec5b3725 100644
--- a/src/arm/lithium-arm.cc
+++ b/src/arm/lithium-arm.cc
@@ -999,7 +999,14 @@ LInstruction* LChunkBuilder::DoThisFunction(HThisFunction* instr) {
 
 
 LInstruction* LChunkBuilder::DoContext(HContext* instr) {
-  return instr->HasNoUses() ? NULL : DefineAsRegister(new(zone()) LContext);
+  // If there is a non-return use, the context must be allocated in a register.
+  for (HUseIterator it(instr->uses()); !it.Done(); it.Advance()) {
+    if (!it.value()->IsReturn()) {
+      return DefineAsRegister(new(zone()) LContext);
+    }
+  }
+
+  return NULL;
 }