Revert of Turn ChannelMojo on Mac and Linux

ipc/mojo/ipc_channel_mojo.cc

Index: ipc/mojo/ipc_channel_mojo.cc
diff --git a/ipc/mojo/ipc_channel_mojo.cc b/ipc/mojo/ipc_channel_mojo.cc
index 45cdc1aafd70f2d3da723663e84c14b5e4fab690..4051bb5c21a87c3ea49811a7f30cfaeea124018f 100644
--- a/ipc/mojo/ipc_channel_mojo.cc
+++ b/ipc/mojo/ipc_channel_mojo.cc
@@ -175,15 +175,8 @@
 
 // static
 bool ChannelMojo::ShouldBeUsed() {
-  // Being conservative, this is currently enabled only on Mac and
-  // Linux even though this should work on all platforms.
-  // TODO(morrita): Turn this on all platform and kill
-  // --enable-renderer-mojo-channel
-#if defined(OS_POSIX) && !defined(OS_ANDROID)
-  return true;
-#else
+  // TODO(morrita): Turn this on for a set of platforms.
   return false;
-#endif
 }
 
 // static