Implementation of PostTaskAndReply() in MessageLoopProxy and BrowserThread.

base/message_loop_proxy.cc

Index: base/message_loop_proxy.cc
diff --git a/base/message_loop_proxy.cc b/base/message_loop_proxy.cc
index a38db393f6e4aa63412455d435804b608f86c682..27c1c0f784c675344ed008589c772067c0957687 100644
--- a/base/message_loop_proxy.cc
+++ b/base/message_loop_proxy.cc
@@ -4,6 +4,8 @@
 
 #include "base/message_loop_proxy.h"
 
+#include "base/bind.h"
+
 namespace base {
 
 MessageLoopProxy::MessageLoopProxy() {
@@ -12,8 +14,65 @@ MessageLoopProxy::MessageLoopProxy() {
 MessageLoopProxy::~MessageLoopProxy() {
 }
 
+bool MessageLoopProxy::PostTaskAndReply(
+    const tracked_objects::Location& from_here,
+    const Closure& task,
+    const Closure& reply) {
+  internal::PostTaskAndReplyRelay* relay =
+      new internal::PostTaskAndReplyRelay(from_here, task, reply);
+  if (!PostTask(from_here, Bind(&internal::PostTaskAndReplyRelay::Run,
+                                Unretained(relay)))) {
+    delete relay;
+    return false;
+  }
+
+  return true;
+}
+
 void MessageLoopProxy::OnDestruct() const {
   delete this;
 }
 
+namespace internal {
+
+PostTaskAndReplyRelay::PostTaskAndReplyRelay(
+    const tracked_objects::Location& from_here,
+    const Closure& task,
+    const Closure& reply)
+    : from_here_(from_here),
+      origin_loop_(MessageLoopProxy::current()) {
+  task_ = task;
+  reply_ = reply;
+}
+
+PostTaskAndReplyRelay::~PostTaskAndReplyRelay() {
+  DCHECK(origin_loop_->BelongsToCurrentThread());
+  task_.Reset();
+  reply_.Reset();
+}
+
+void PostTaskAndReplyRelay::Run() {
+  task_.Run();
+  origin_loop_->PostTask(
+      from_here_,
+      Bind(&PostTaskAndReplyRelay::RunReplyAndSelfDestruct,
+           base::Unretained(this)));
+}
+
+void PostTaskAndReplyRelay::RunReplyAndSelfDestruct() {
+  DCHECK(origin_loop_->BelongsToCurrentThread());
+
+  // Force |task_| to be released before |reply_| is to ensure that no one
+  // accidentally depends on |task_| keeping one of its arguments alive while
+  // |reply_| is executing.
+  task_.Reset();
+
+  reply_.Run();
+
+  // Cue mission impossible theme.
+  delete this;
+}
+
+}  // namespace internal
+
 }  // namespace base