Revert of Revert of IPC::ChannelMojo: Make IPC handling robust agains…

…t bad messages. (patchset chromium#1 id:1 of https://codereview.chromium.org/883373002/)

Reason for revert:
Wrong revert, ipc fuzzer broke because of something else.

Original issue's description:
> Revert of IPC::ChannelMojo: Make IPC handling robust against bad messages. (patchset chromium#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
>
> Committed: https://crrev.com/726621f93d2802dfc2c90732c7133145c9854e38
> Cr-Commit-Position: refs/heads/master@{#313778}

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

Review URL: https://codereview.chromium.org/892503002

Cr-Commit-Position: refs/heads/master@{#313780}

ipc/mojo/ipc_mojo_bootstrap.cc

@@ -100,9 +100,14 @@ void MojoServerBootstrap::OnChannelConnected(int32 peer_pid) {
 }
 
 bool MojoServerBootstrap::OnMessageReceived(const Message&) {
-  DCHECK_EQ(state(), STATE_WAITING_ACK);
-  set_state(STATE_READY);
+  if (state() != STATE_WAITING_ACK) {
+    set_state(STATE_ERROR);
+    LOG(ERROR) << "Got inconsistent message from client.";
+    return false;
+  }
 
+  set_state(STATE_READY);
+  CHECK(server_pipe_.is_valid());
   delegate()->OnPipeAvailable(
       mojo::embedder::ScopedPlatformHandle(server_pipe_.release()));
 
@@ -129,6 +134,12 @@ 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

@@ -55,6 +55,9 @@ 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_; }