Make saving and restoring of the context around closure calls explicit.

vm/flow_graph_compiler_x64.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/globals.h"  // Needed here to get TARGET_ARCH_X64.
 #if defined(TARGET_ARCH_X64)
 
 #include "vm/flow_graph_compiler.h"
 
 #include "lib/error.h"
@@ skipping 511 matching lines @@
   __ movq(RAX, CTX);
 }
 
 
 void FlowGraphCompiler::VisitStoreContext(StoreContextComp* comp) {
   LoadValue(CTX, comp->value());
 }
 
 
 void FlowGraphCompiler::VisitClosureCall(ClosureCallComp* comp) {
-  ASSERT(comp->context()->IsUse());
   ASSERT(VerifyCallComputation(comp));
   // The arguments to the stub include the closure.  The arguments
   // descriptor describes the closure's arguments (and so does not include
   // the closure).
   int argument_count = comp->ArgumentCount();
   const Array& arguments_descriptor =
       CodeGenerator::ArgumentsDescriptor(argument_count - 1,
                                          comp->argument_names());
   __ LoadObject(R10, arguments_descriptor);
 
   GenerateCall(comp->token_index(),
                comp->try_index(),
                &StubCode::CallClosureFunctionLabel(),
                PcDescriptors::kOther);
   __ Drop(argument_count);
-  __ popq(CTX);
 }
 
 
 void FlowGraphCompiler::VisitInstanceCall(InstanceCallComp* comp) {
   ASSERT(VerifyCallComputation(comp));
   EmitInstanceCall(comp->cid(),
                    comp->token_index(),
                    comp->try_index(),
                    comp->function_name(),
                    comp->ArgumentCount(),
@@ skipping 1184 matching lines @@
 
 
 void FlowGraphCompiler::FinalizeComments(const Code& code) {
   code.set_comments(assembler_->GetCodeComments());
 }
 
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_X64