Disable mojo unittest flaky on Android.

Disabled test:
MultiprocessMessagePipeTestWithPeerSupport.ChannelPipesWithMultipleChildren

TBR=rockot@chromium.org

Bug: 905620
Change-Id: I228040b5c07a420beae202da43887c0db17d0e27
Reviewed-on: https://chromium-review.googlesource.com/c/1337619Reviewed-by: Arthur Sonzogni <arthursonzogni@chromium.org>
Commit-Queue: Arthur Sonzogni <arthursonzogni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#608344}

mojo/core/multiprocess_message_pipe_unittest.cc

@@ -871,8 +871,15 @@ TEST_P(MultiprocessMessagePipeTestWithPeerSupport,
   CloseHandle(echo_proxy_c);
 }
 
+// Flaky on Android. See https://crbug.com/905620.
+#if defined(OS_ANDROID)
+#define MAYBE_ChannelPipesWithMultipleChildren \
+  DISABLED_ChannelPipesWithMultipleChildren
+#else
+#define MAYBE_ChannelPipesWithMultipleChildren ChannelPipesWithMultipleChildren
+#endif
 TEST_P(MultiprocessMessagePipeTestWithPeerSupport,
-       ChannelPipesWithMultipleChildren) {
+       MAYBE_ChannelPipesWithMultipleChildren) {
   RunTestClient("ChannelEchoClient", [&](MojoHandle a) {
     RunTestClient("ChannelEchoClient", [&](MojoHandle b) {
       VerifyEcho(a, "hello child 0");