Revert of IPC::ChannelMojo: Make IPC handling robust against bad messages. (patchset #3 id:40001 of https://codereview.chromium.org/725733002/)

Reason for revert:
Broke ipc fuzzer

Original issue's description:
> IPC::ChannelMojo: Make IPC handling robust against bad messages.
>
> This change replaces some DCHECK()s with real error handling.
> They happen when it receives broken messages.
>
> BUG=428800
> [email protected]
>
> Committed: https://crrev.com/185ffdf58f85e47db9666d2ad9b80ff9bd7fa54b
> Cr-Commit-Position: refs/heads/master@{#304102}

[email protected],[email protected]
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=428800

Review URL: https://codereview.chromium.org/883373002

Cr-Commit-Position: refs/heads/master@{#313778}
diff --git a/ipc/mojo/ipc_mojo_bootstrap.cc b/ipc/mojo/ipc_mojo_bootstrap.cc
index 591ced0..b34648b 100644
--- a/ipc/mojo/ipc_mojo_bootstrap.cc
+++ b/ipc/mojo/ipc_mojo_bootstrap.cc
@@ -100,14 +100,9 @@
 }
 
 bool MojoServerBootstrap::OnMessageReceived(const Message&) {
-  if (state() != STATE_WAITING_ACK) {
-    set_state(STATE_ERROR);
-    LOG(ERROR) << "Got inconsistent message from client.";
-    return false;
-  }
-
+  DCHECK_EQ(state(), STATE_WAITING_ACK);
   set_state(STATE_READY);
-  CHECK(server_pipe_.is_valid());
+
   delegate()->OnPipeAvailable(
       mojo::embedder::ScopedPlatformHandle(server_pipe_.release()));
 
@@ -134,12 +129,6 @@
 }
 
 bool MojoClientBootstrap::OnMessageReceived(const Message& message) {
-  if (state() != STATE_INITIALIZED) {
-    set_state(STATE_ERROR);
-    LOG(ERROR) << "Got inconsistent message from server.";
-    return false;
-  }
-
   PlatformFileForTransit pipe;
   PickleIterator iter(message);
   if (!ParamTraits<PlatformFileForTransit>::Read(&message, &iter, &pipe)) {