Ignore stderr failure messages on iossim when not running xctests.

testing/iossim/iossim.mm

Index: testing/iossim/iossim.mm
diff --git a/testing/iossim/iossim.mm b/testing/iossim/iossim.mm
index 3c1e353eeae30918d9da25c6deb7af088068e7f9..a1b174c4fa8bfc4c759d6122413fa8de4e2d74e0 100644
--- a/testing/iossim/iossim.mm
+++ b/testing/iossim/iossim.mm
@@ -258,6 +258,24 @@ void RunApplication(NSString* app_path,
     [@"platform=iOS Simulator,id=" stringByAppendingString:udid],
     @"test-without-building"
   ]] autorelease];
+
+  // The following stderr messages are meaningless on iossim when not running
+  // xctests and can be safely stripped.
+  if (!xctest_path) {
+    NSPipe* stderr_pipe = [NSPipe pipe];
+    stderr_pipe.fileHandleForReading.readabilityHandler =
+        ^(NSFileHandle* handle) {
+          NSString* log = [[[NSString alloc] initWithData:handle.availableData
+                                                 encoding:NSUTF8StringEncoding]
+              autorelease];
+          if ([log containsString:@"IDETestOperationsObserverErrorDomain"] ||
+              [log containsString:@"** TEST EXECUTE FAILED **"]) {
+            return;
+          }
+          printf("%s", [log UTF8String]);
+        };
+    [task setStandardError:stderr_pipe];
+  }
   [task run];
 }