[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 d04edaf580a92a1c1f7ec10a8befcbb5eb0763b3..bc96a5ffc69466cd820231963baaadb1bfd010b1 100644
--- a/mojo/edk/system/channel_win.cc
+++ b/mojo/edk/system/channel_win.cc
@@ -85,6 +85,8 @@ class ChannelWin : public Channel,
 
     memset(&write_context_, 0, sizeof(write_context_));
     write_context_.handler = this;
+
+    wait_for_connect_ = handle_.get().needs_connection;
   }
 
   void Start() override {
@@ -148,6 +150,29 @@ class ChannelWin : public Channel,
     base::MessageLoopForIO::current()->RegisterIOHandler(
         handle_.get().handle, this);
 
+    if (wait_for_connect_) {
+      BOOL ok = ConnectNamedPipe(handle_.get().handle,
+                                 &read_context_.overlapped);

[Ken Rockot(use gerrit already), 2016/05/10 22:41:28]

I'd rather we use a separate IO context for connection events. That makes
OnIOCompleted easier to understand

[Anand Mistry (off Chromium), 2016/05/11 04:15:20]

Done.

+      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_);
@@ -191,7 +216,18 @@ class ChannelWin : public Channel,
     if (error != ERROR_SUCCESS) {
       OnError();
     } else if (context == &read_context_) {
-      OnReadDone(static_cast<size_t>(bytes_transfered));
+      if (wait_for_connect_) {
+        wait_for_connect_ = false;
+        ReadMore(0);
+
+        base::AutoLock lock(write_lock_);
+        if (delay_writes_) {
+          delay_writes_ = false;
+          WriteNextNoLock();
+        }
+      } else {
+        OnReadDone(static_cast<size_t>(bytes_transfered));
+      }
     } else {
       CHECK(context == &write_context_);
       OnWriteDone(static_cast<size_t>(bytes_transfered));
@@ -309,6 +345,8 @@ class ChannelWin : public Channel,
   // TODO(amistry): Remove before M50 branch point.
   uintptr_t sentinel_;
 
+  bool wait_for_connect_;
+
   DISALLOW_COPY_AND_ASSIGN(ChannelWin);
 };