Revert of Disable two tests in mojo_system_unittests that are suspected to be timing out (patchset #2 id:20001 of https://codereview.chromium.org/2497203002/ )

Reason for revert:
Issue 663998 still persists after this CL.

Original issue's description:
> Disable two tests in mojo_system_unittests that are suspected to be timing out
>
> BUG=663998
> TBR=pdr@chromium.org, timloh@chromium.org
>
> Committed: https://crrev.com/aae520affa1d2c4397bf4d4758a9ff48d5a0cc88
> Cr-Commit-Position: refs/heads/master@{#431847}

TBR=
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=663998

Review-Url: https://codereview.chromium.org/2504533002
Cr-Commit-Position: refs/heads/master@{#432117}


CrOS-Libchrome-Original-Commit: ba86cdb48c680aa78a142dee329d1c57ba22b00a
diff --git a/mojo/edk/embedder/embedder_unittest.cc b/mojo/edk/embedder/embedder_unittest.cc
index f371f2a..4521f80 100644
--- a/mojo/edk/embedder/embedder_unittest.cc
+++ b/mojo/edk/embedder/embedder_unittest.cc
@@ -224,15 +224,7 @@
                                      nullptr));
 }
 
-#if defined(OS_ANDROID)
-// This test is suspected to be flaky on android https://crbug.com/663998.
-#define MAYBE_PipeSetup_LaunchFailure \
-    DISABLED_PipeSetup_LaunchFailure
-#else
-#define MAYBE_PipeSetup_LaunchFailure \
-    PipeSetup_LaunchFailure
-#endif
-TEST_F(EmbedderTest, MAYBE_PipeSetup_LaunchFailure) {
+TEST_F(EmbedderTest, PipeSetup_LaunchFailure) {
   PlatformChannelPair pair;
 
   std::string child_token = GenerateRandomToken();
diff --git a/mojo/edk/system/multiprocess_message_pipe_unittest.cc b/mojo/edk/system/multiprocess_message_pipe_unittest.cc
index 897c6d9..011d824 100644
--- a/mojo/edk/system/multiprocess_message_pipe_unittest.cc
+++ b/mojo/edk/system/multiprocess_message_pipe_unittest.cc
@@ -875,9 +875,6 @@
   CloseHandle(echo_proxy_c);
 }
 
-#if !defined(OS_ANDROID)
-// This test is suspected to be flaky on android https://crbug.com/663998
-// and thus disabled on android.
 TEST_P(MultiprocessMessagePipeTestWithPeerSupport,
        ChannelPipesWithMultipleChildren) {
   RUN_CHILD_ON_PIPE(ChannelEchoClient, a)
@@ -890,7 +887,6 @@
     END_CHILD()
   END_CHILD()
 }
-#endif
 
 // Reads and turns a pipe handle some number of times to create lots of
 // transient proxies.