Introduce a hydrogen value for contexts, support context slot assignment.

src/hydrogen-instructions.cc

Index: src/hydrogen-instructions.cc
diff --git a/src/hydrogen-instructions.cc b/src/hydrogen-instructions.cc
index c24ddfc80c94dc17c51cad5be25693cb8ea2d9f5..0ff41ba2388fb7cd34376a1e19e26d472904d9dc 100644
--- a/src/hydrogen-instructions.cc
+++ b/src/hydrogen-instructions.cc
@@ -1193,7 +1193,15 @@ void HStoreGlobal::PrintDataTo(StringStream* stream) const {
 
 
 void HLoadContextSlot::PrintDataTo(StringStream* stream) const {
-  stream->Add("(%d, %d)", context_chain_length(), slot_index());
+  value()->PrintNameTo(stream);
+  stream->Add("[%d]", slot_index());
+}
+
+
+void HStoreContextSlot::PrintDataTo(StringStream* stream) const {
+  context()->PrintNameTo(stream);
+  stream->Add("[%d] = ", slot_index());
+  value()->PrintNameTo(stream);
 }