Limit the behavior of some tests to avoid OS X flake

mojo/edk/embedder/platform_channel_pair_posix_unittest.cc

Index: mojo/edk/embedder/platform_channel_pair_posix_unittest.cc
diff --git a/mojo/edk/embedder/platform_channel_pair_posix_unittest.cc b/mojo/edk/embedder/platform_channel_pair_posix_unittest.cc
index 56540d79c106a835d349d29fbac2e6670b14b8dc..107406e20e859523de7e38f5d8f82d8f3380fb96 100644
--- a/mojo/edk/embedder/platform_channel_pair_posix_unittest.cc
+++ b/mojo/edk/embedder/platform_channel_pair_posix_unittest.cc
@@ -137,7 +137,14 @@ TEST_F(PlatformChannelPairPosixTest, SendReceiveFDs) {
   ScopedPlatformHandle server_handle = channel_pair.PassServerHandle().Pass();
   ScopedPlatformHandle client_handle = channel_pair.PassClientHandle().Pass();
 
-  for (size_t i = 1; i < kPlatformChannelMaxNumHandles; i++) {
+// Reduce the number of FDs opened on OS X to avoid test flake.
+#if defined(OS_MACOSX)
+  const size_t kNumHandlesToSend = kPlatformChannelMaxNumHandles / 2;
+#else
+  const size_t kNumHandlesToSend = kPlatformChannelMaxNumHandles;
+#endif
+
+  for (size_t i = 1; i < kNumHandlesToSend; i++) {
     // Make |i| files, with the j-th file consisting of j copies of the digit
     // |c|.
     const char c = '0' + (i % 10);
@@ -178,7 +185,7 @@ TEST_F(PlatformChannelPairPosixTest, SendReceiveFDs) {
       received_handles.pop_front();
       ASSERT_TRUE(fp);
       rewind(fp.get());
-      char read_buf[kPlatformChannelMaxNumHandles];
+      char read_buf[kNumHandlesToSend];
       size_t bytes_read = fread(read_buf, 1, sizeof(read_buf), fp.get());
       EXPECT_EQ(j + 1, bytes_read);
       EXPECT_EQ(std::string(j + 1, c), std::string(read_buf, bytes_read));