Merge "Fix a bug in the implementation of Mach shared memory." to M48.

> The bug prevented Mach shared memory from being mapped, after being unmapped.
>
> BUG=466437
>
> Review URL: https://codereview.chromium.org/1452063003
>
> Cr-Commit-Position: refs/heads/master@{#360192}

(cherry picked from commit 8d84ed5)
TBR=mark@chromium.org
BUG=563762

Review URL: https://codereview.chromium.org/1487203002 .

Cr-Commit-Position: refs/branch-heads/2564@{#188}
Cr-Branched-From: 1283eca-refs/heads/master@{#359700}

base/memory/shared_memory_mac.cc

@@ -368,15 +368,17 @@ bool SharedMemory::Unmap() {
   switch (mapped_memory_mechanism_) {
     case SharedMemoryHandle::POSIX:
       munmap(memory_, mapped_size_);
-      memory_ = NULL;
-      mapped_size_ = 0;
-      return true;
+      break;
     case SharedMemoryHandle::MACH:
       mach_vm_deallocate(mach_task_self(),
                          reinterpret_cast<mach_vm_address_t>(memory_),
                          mapped_size_);
-      return true;
+      break;
   }
+
+  memory_ = NULL;
+  mapped_size_ = 0;
+  return true;
 }
 
 SharedMemoryHandle SharedMemory::handle() const {

base/memory/shared_memory_mac_unittest.cc

@@ -337,6 +337,21 @@ TEST_F(SharedMemoryMacMultiProcessTest, MachDuplicateAndClose) {
   EXPECT_EQ(active_name_count, GetActiveNameCount());
 }
 
+// Tests that Mach shared memory can be mapped and unmapped.
+TEST_F(SharedMemoryMacMultiProcessTest, MachUnmapMap) {
+  // Mach-based SharedMemory isn't support on OSX 10.6.
+  if (mac::IsOSSnowLeopard())
+    return;
+
+  mach_msg_type_number_t active_name_count = GetActiveNameCount();
+
+  scoped_ptr<SharedMemory> shared_memory = CreateSharedMemory(s_memory_size);
+  ASSERT_TRUE(shared_memory->Unmap());
+  ASSERT_TRUE(shared_memory->Map(s_memory_size));
+  shared_memory.reset();
+  EXPECT_EQ(active_name_count, GetActiveNameCount());
+}
+
 // Tests that passing a SharedMemoryHandle to a SharedMemory object also passes
 // ownership, and that destroying the SharedMemory closes the SharedMemoryHandle
 // as well.