Revert "Handle error return from zygote recvmsg call."

This reverts commit 86ed44e0.

Reason for revert: Blocking revert of r554902.

Original change's description:
> Handle error return from zygote recvmsg call.
> 
> This trips a check far away from the actual issue. The CHECK is too
> strong and prevents executing the error handling path beneath it.
> 
> Shuffle a few blocks and comments around so that the flow makes
> more sense and is easier to read, and initial fork failures are
> caught earlier.
> 
> Bug: 835778
> Change-Id: I46b960f9fd1095f5fc5224bf9cc80703e8fc325f
> Reviewed-on: https://chromium-review.googlesource.com/1030876
> Commit-Queue: Tom Sepez <tsepez@chromium.org>
> Reviewed-by: Daniel Cheng <dcheng@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#554949}

TBR=dcheng@chromium.org,jln@chromium.org,jam@chromium.org,tsepez@chromium.org

Change-Id: I877d3610bd75eaa1176189319923bcc75b794781
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 835778, 838498
Reviewed-on: https://chromium-review.googlesource.com/1036983Reviewed-by: Matt Giuca <mgiuca@chromium.org>
Commit-Queue: Matt Giuca <mgiuca@chromium.org>
Cr-Commit-Position: refs/heads/master@{#554999}

services/service_manager/zygote/zygote_linux.cc

@@ -438,8 +438,6 @@ int Zygote::ForkWithRealPid(const std::string& process_type,
   }
 
   if (pid == 0) {
-    // In the child process.
-
     // If the process is the init process inside a PID namespace, it must have
     // explicit signal handlers.
     if (getpid() == 1) {
@@ -451,6 +449,7 @@ int Zygote::ForkWithRealPid(const std::string& process_type,
       }
     }
 
+    // In the child process.
     write_pipe.reset();
 
     // Ping the PID oracle socket so the browser can find our PID.
@@ -477,34 +476,32 @@ int Zygote::ForkWithRealPid(const std::string& process_type,
   }
 
   // In the parent process.
-  if (pid < 0) {
-    // Fork failed.
-    return -1;
-  }
-
   read_pipe.reset();
   pid_oracle.reset();
 
   // Always receive a real PID from the zygote host, though it might
   // be invalid (see below).
-  base::ProcessId real_pid = -1;
+  base::ProcessId real_pid;
   {
     std::vector<base::ScopedFD> recv_fds;
     char buf[kZygoteMaxMessageLength];
     const ssize_t len = base::UnixDomainSocket::RecvMsg(
         kZygoteSocketPairFd, buf, sizeof(buf), &recv_fds);
+    CHECK_GT(len, 0);
+    CHECK(recv_fds.empty());
 
-    if (len > 0) {
-      CHECK(recv_fds.empty());
+    base::Pickle pickle(buf, len);
+    base::PickleIterator iter(pickle);
 
-      base::Pickle pickle(buf, len);
-      base::PickleIterator iter(pickle);
+    int kind;
+    CHECK(iter.ReadInt(&kind));
+    CHECK(kind == kZygoteCommandForkRealPID);
+    CHECK(iter.ReadInt(&real_pid));
+  }
 
-      int kind;
-      CHECK(iter.ReadInt(&kind));
-      CHECK(kind == kZygoteCommandForkRealPID);
-      CHECK(iter.ReadInt(&real_pid));
-    }
+  // Fork failed.
+  if (pid < 0) {
+    return -1;
   }
 
   // If we successfully forked a child, but it crashed without sending