Code:   void Initialized(mojo::ScopedSharedBufferHandle shared_buffer,
                   mojo::ScopedHandle socket_handle,
                   bool initially_muted) {
    ASSERT_TRUE(shared_buffer.is_valid());
    ASSERT_TRUE(socket_handle.is_valid());

    base::PlatformFile fd;
    mojo::UnwrapPlatformFile(std::move(socket_handle), &fd);
    socket_ = std::make_unique<base::CancelableSyncSocket>(fd);
    EXPECT_NE(socket_->handle(), base::CancelableSyncSocket::kInvalidHandle);
 
     size_t memory_length;
     base::SharedMemoryHandle shmem_handle;
    bool read_only;
     EXPECT_EQ(
         mojo::UnwrapSharedMemoryHandle(std::move(shared_buffer), &shmem_handle,
                                       &memory_length, &read_only),
         MOJO_RESULT_OK);
    EXPECT_TRUE(read_only);
    buffer_ = std::make_unique<base::SharedMemory>(shmem_handle, read_only);
 
     GotNotification(initially_muted);
   }

Vulnerability Type: 
CWE ID: CWE-787
Summary: Incorrect use of mojo::WrapSharedMemoryHandle in Mojo in Google Chrome prior to 65.0.3325.146 allowed a remote attacker who had compromised the renderer process to perform an out of bounds memory write via a crafted HTML page.
Commit Message: Correct mojo::WrapSharedMemoryHandle usage

Fixes some incorrect uses of mojo::WrapSharedMemoryHandle which
were assuming that the call actually has any control over the memory
protection applied to a handle when mapped.

Where fixing usage is infeasible for this CL, TODOs are added to
annotate follow-up work.

Also updates the API and documentation to (hopefully) improve clarity
and avoid similar mistakes from being made in the future.

BUG=792900

Cq-Include-Trybots: master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
Change-Id: I0578aaa9ca3bfcb01aaf2451315d1ede95458477
Reviewed-on: https://chromium-review.googlesource.com/818282
Reviewed-by: Wei Li <weili@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Reviewed-by: Yuzhu Shen <yzshen@chromium.org>
Reviewed-by: Robert Sesek <rsesek@chromium.org>
Commit-Queue: Ken Rockot <rockot@chromium.org>
Cr-Commit-Position: refs/heads/master@{#530268}