IPC::ChannelMojo: Don't supress MOJO_RESULT_FAILED_PRECONDITION

The error should be reported to IPC::Listener as it is a
signal of the dead peer. Without this, the browser cannot
detect renderer crashes.

TEST=browser_tests (with ChannelMojo enabled)
R=viettrungluu@chromium.org,darin@chromium.org
BUG=none

Review URL: https://codereview.chromium.org/453643003

Cr-Commit-Position: refs/heads/master@{#288442}
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@288442 0039d316-1c4b-4281-b951-d872f2087c98

ipc/mojo/ipc_channel_mojo_unittest.cc

@@ -22,7 +22,8 @@ namespace {
 
 class ListenerThatExpectsOK : public IPC::Listener {
  public:
-  ListenerThatExpectsOK() {}
+  ListenerThatExpectsOK()
+      : received_ok_(false) {}
 
   virtual ~ListenerThatExpectsOK() {}
 
@@ -31,12 +32,16 @@ class ListenerThatExpectsOK : public IPC::Listener {
     std::string should_be_ok;
     EXPECT_TRUE(iter.ReadString(&should_be_ok));
     EXPECT_EQ(should_be_ok, "OK");
+    received_ok_ = true;
     base::MessageLoop::current()->Quit();
     return true;
   }
 
   virtual void OnChannelError() OVERRIDE {
-    NOTREACHED();
+    // The connection should be healthy while the listener is waiting
+    // message.  An error can occur after that because the peer
+    // process dies.
+    DCHECK(received_ok_);
   }
 
   static void SendOK(IPC::Sender* sender) {
@@ -45,6 +50,9 @@ class ListenerThatExpectsOK : public IPC::Listener {
     message->WriteString(std::string("OK"));
     ASSERT_TRUE(sender->Send(message));
   }
+
+ private:
+  bool received_ok_;
 };
 
 class ListenerThatShouldBeNeverCalled : public IPC::Listener {

ipc/mojo/ipc_message_pipe_reader.cc

@@ -67,12 +67,12 @@ void MessagePipeReader::PipeIsReady(MojoResult wait_result) {
   pipe_wait_id_ = 0;
 
   if (wait_result != MOJO_RESULT_OK) {
-    // FAILED_PRECONDITION happens when the pipe is
-    // closed before the waiter is scheduled in a backend thread.
-    if (wait_result != MOJO_RESULT_ABORTED &&
-        wait_result != MOJO_RESULT_FAILED_PRECONDITION) {
-      DLOG(WARNING) << "Pipe got error from the waiter. Closing: "
-                    << wait_result;
+    if (wait_result != MOJO_RESULT_ABORTED) {
+      // FAILED_PRECONDITION happens every time the peer is dead so
+      // it isn't worth polluting the log message.
+      DLOG_IF(WARNING, wait_result != MOJO_RESULT_FAILED_PRECONDITION)
+          << "Pipe got error from the waiter. Closing: "
+          << wait_result;
       OnPipeError(wait_result);
     }