Code:     memory_handle(const media::BitstreamBuffer& input) {
  base::SharedMemoryHandle input_handle =
      base::SharedMemory::DuplicateHandle(input.handle());
  if (!base::SharedMemory::IsHandleValid(input_handle)) {
     DLOG(ERROR) << "Failed to duplicate handle of BitstreamBuffer";
     return mojo::ScopedSharedBufferHandle();
   }
  return mojo::WrapSharedMemoryHandle(input_handle, input.size(),
                                      true /* read_only */);
 }

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}
CWE ID: CWE-787
    memory_handle(const media::BitstreamBuffer& input) {
  base::SharedMemoryHandle input_handle =
      base::SharedMemory::DuplicateHandle(input.handle());
  if (!base::SharedMemory::IsHandleValid(input_handle)) {
     DLOG(ERROR) << "Failed to duplicate handle of BitstreamBuffer";
     return mojo::ScopedSharedBufferHandle();
   }

  // TODO(https://crbug.com/793446): Update this to |kReadOnly| protection once
  // BitstreamBuffer can guarantee that its handle() field always corresponds to
  // a read-only SharedMemoryHandle.
  return mojo::WrapSharedMemoryHandle(
      input_handle, input.size(),
      mojo::UnwrappedSharedMemoryHandleProtection::kReadWrite);
 }
