Make GlobalDescriptors::MaybeGet return -1 when the key is not found.

ipc/ipc_send_fds_test.cc

Index: ipc/ipc_send_fds_test.cc
diff --git a/ipc/ipc_send_fds_test.cc b/ipc/ipc_send_fds_test.cc
index 124a3dcb09271617182563c43f6f09e7c3423194..a339a79da1e777244e96785f4ce8b8e798f1b983 100644
--- a/ipc/ipc_send_fds_test.cc
+++ b/ipc/ipc_send_fds_test.cc
@@ -22,6 +22,8 @@ extern "C" {
 
 #if defined(OS_POSIX)
 #include "base/file_descriptor_posix.h"
+#include "base/global_descriptors_posix.h"
+#include "ipc/ipc_descriptors.h"
 
 namespace {
 
@@ -132,7 +134,8 @@ int TestDescriptorClient(ino_t expected_inode_num) {
 // ---------------------------------------------------------------------------
 #if defined(OS_MACOSX)
 // TODO(port): Make this test cross-platform.
-MULTIPROCESS_TEST_MAIN(RunTestDescriptorClientSandboxed) {
+MULTIPROCESS_TEST_MAIN(RunTestDescriptorClientSandboxed,
+                       MultiProcessTestIPCSetUp) {
   struct stat st;
   const int fd = open(kDevZeroPath, O_RDONLY);
   fstat(fd, &st);
@@ -177,7 +180,7 @@ TEST_F(IPCChannelTest, DescriptorTestSandboxed) {
 }
 #endif  // defined(OS_MACOSX)
 
-MULTIPROCESS_TEST_MAIN(RunTestDescriptorClient) {
+MULTIPROCESS_TEST_MAIN(RunTestDescriptorClient, MultiProcessTestIPCSetUp) {
   struct stat st;
   const int fd = open(kDevZeroPath, O_RDONLY);
   fstat(fd, &st);