Revert of IPC::ChannelMojo: Make IPC handling robust against bad messages....

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
> R=viettrungluu@chromium.org
>
> Committed: https://crrev.com/185ffdf58f85e47db9666d2ad9b80ff9bd7fa54b
> Cr-Commit-Position: refs/heads/master@{#304102}

TBR=viettrungluu@chromium.org,morrita@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=428800

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

Cr-Commit-Position: refs/heads/master@{#313778}

ipc/mojo/ipc_mojo_bootstrap.cc

@@ -100,14 +100,9 @@ void MojoServerBootstrap::OnChannelConnected(int32 peer_pid) {
 }
 
 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 @@ MojoClientBootstrap::MojoClientBootstrap() {
 }
 
 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)) {

ipc/mojo/ipc_mojo_bootstrap.h

@@ -55,9 +55,6 @@ class IPC_MOJO_EXPORT MojoBootstrap : public Listener {
 #endif  // defined(OS_POSIX) && !defined(OS_NACL)
 
  protected:
-  // On MojoServerBootstrap: INITIALIZED -> WAITING_ACK -> READY
-  // On MojoClientBootstrap: INITIALIZED -> READY
-  // STATE_ERROR is a catch-all state that captures any observed error.
   enum State { STATE_INITIALIZED, STATE_WAITING_ACK, STATE_READY, STATE_ERROR };
 
   Delegate* delegate() const { return delegate_; }