media/base WritableUnalignedMapping fix.

Use the underlying handle size when wrapping a legacy shared memory instance.

Bug: 849207
Change-Id: Ibbf62ebbea5a95d64d84a0faf2042f639be5b820
Reviewed-on: https://chromium-review.googlesource.com/1118268Reviewed-by: Alexandr Ilin <alexilin@chromium.org>
Reviewed-by: Dan Sanders <sandersd@chromium.org>
Commit-Queue: Matthew Cary <mattcary@chromium.org>
Cr-Commit-Position: refs/heads/master@{#571846}

media/base/unaligned_shared_memory.cc

@@ -115,7 +115,7 @@ WritableUnalignedMapping::WritableUnalignedMapping(
     : WritableUnalignedMapping(
           mojo::UnwrapUnsafeSharedMemoryRegion(mojo::WrapSharedMemoryHandle(
               handle,
-              size,
+              handle.GetSize(),
               mojo::UnwrappedSharedMemoryHandleProtection::kReadWrite)),
           size,
           offset) {}

media/base/unaligned_shared_memory_unittest.cc

@@ -129,6 +129,13 @@ TEST(WritableUnalignedMappingTest, Map_Unaligned) {
   EXPECT_EQ(0, memcmp(shm.memory(), kData, kDataSize));
 }
 
+TEST(WritableUnalignedMappingTest, Map_UnalignedHandle) {
+  auto region = CreateHandle(kUnalignedData, kUnalignedDataSize);
+  WritableUnalignedMapping shm(region, kDataSize, kUnalignedOffset);
+  ASSERT_TRUE(shm.IsValid());
+  EXPECT_EQ(0, memcmp(shm.memory(), kData, kDataSize));
+}
+
 TEST(WritableUnalignedMappingTest, Map_InvalidRegion) {
   base::UnsafeSharedMemoryRegion region;
   WritableUnalignedMapping shm(region, kDataSize, 0);