[mojo] Use a pipe path to initialise Mojo in elevated utility processes.

mojo/edk/system/channel_win.cc

Index: mojo/edk/system/channel_win.cc
diff --git a/mojo/edk/system/channel_win.cc b/mojo/edk/system/channel_win.cc
index 38744ab99b16e424daf497b24695fc17469c1e0b..5d0b0cfc6285eb861d1bf984a377d6e95b2c3f9c 100644
--- a/mojo/edk/system/channel_win.cc
+++ b/mojo/edk/system/channel_win.cc
@@ -80,6 +80,8 @@ class ChannelWin : public Channel,
         handle_(std::move(handle)),
         io_task_runner_(io_task_runner) {
     CHECK(handle_.is_valid());
+
+    wait_for_connect_ = handle_.get().needs_connection;
   }
 
   void Start() override {
@@ -139,6 +141,29 @@ class ChannelWin : public Channel,
     base::MessageLoopForIO::current()->RegisterIOHandler(
         handle_.get().handle, this);
 
+    if (wait_for_connect_) {
+      BOOL ok = ConnectNamedPipe(handle_.get().handle,
+                                 &connect_context_.overlapped);
+      if (ok) {
+        PLOG(ERROR) << "Unexpected success while waiting for pipe connection";
+        OnError();
+        return;
+      }
+
+      const DWORD err = GetLastError();
+      switch (err) {
+        case ERROR_PIPE_CONNECTED:
+          wait_for_connect_ = false;
+          break;
+        case ERROR_IO_PENDING:
+          AddRef();
+          return;
+        case ERROR_NO_DATA:
+          OnError();
+          return;
+      }
+    }
+
     // Now that we have registered our IOHandler, we can start writing.
     {
       base::AutoLock lock(write_lock_);
@@ -179,6 +204,16 @@ class ChannelWin : public Channel,
                      DWORD error) override {
     if (error != ERROR_SUCCESS) {
       OnError();
+    } else if (context == &connect_context_) {
+      DCHECK(wait_for_connect_);
+      wait_for_connect_ = false;
+      ReadMore(0);
+
+      base::AutoLock lock(write_lock_);
+      if (delay_writes_) {
+        delay_writes_ = false;
+        WriteNextNoLock();
+      }
     } else if (context == &read_context_) {
       OnReadDone(static_cast<size_t>(bytes_transfered));
     } else {
@@ -277,6 +312,7 @@ class ChannelWin : public Channel,
   ScopedPlatformHandle handle_;
   scoped_refptr<base::TaskRunner> io_task_runner_;
 
+  base::MessageLoopForIO::IOContext connect_context_;
   base::MessageLoopForIO::IOContext read_context_;
   base::MessageLoopForIO::IOContext write_context_;
 
@@ -288,6 +324,8 @@ class ChannelWin : public Channel,
   bool reject_writes_ = false;
   std::deque<MessageView> outgoing_messages_;
 
+  bool wait_for_connect_;
+
   DISALLOW_COPY_AND_ASSIGN(ChannelWin);
 };