Use ARGB8888 for a dummy buffer for protected content playbkack on ARC++

We have specified R8 format for a dummy buffer for protected content playback
on ARC++.
R8 format is not supported on exynos device. It leads crash on the devices.
ARGB8888 should be used instead, which is widely supported on all Chrome OS
device.

BUG=chromium:787660, chromium:887658
TEST=No crash on peach_pit and Protected content playback on veyron_minnie and eve

Change-Id: Ia550277ad30a0e0fd814106a1610b59a1a86bb03
Reviewed-on: https://chromium-review.googlesource.com/1242564
Commit-Queue: Hirokazu Honda <hiroh@chromium.org>
Reviewed-by: Pawel Osciak <posciak@chromium.org>
Cr-Commit-Position: refs/heads/master@{#593842}

components/arc/video_accelerator/protected_buffer_manager.cc

@@ -23,7 +23,7 @@ namespace arc {
 
 namespace {
 // Size of the pixmap to be used as the dummy handle for protected buffers.
-constexpr gfx::Size kDummyBufferSize(32, 32);
+constexpr gfx::Size kDummyBufferSize(16, 16);
 
 // Maximum number of concurrent ProtectedBufferAllocatorImpl instances.
 // Currently we have no way to know the resources of ProtectedBufferAllocator.
@@ -463,8 +463,8 @@ scoped_refptr<gfx::NativePixmap> ProtectedBufferManager::ImportDummyFd(
   ui::SurfaceFactoryOzone* factory = platform->GetSurfaceFactoryOzone();
   scoped_refptr<gfx::NativePixmap> pixmap =
       factory->CreateNativePixmapForProtectedBufferHandle(
-          gfx::kNullAcceleratedWidget, kDummyBufferSize, gfx::BufferFormat::R_8,
-          pixmap_handle);
+          gfx::kNullAcceleratedWidget, kDummyBufferSize,
+          gfx::BufferFormat::RGBA_8888, pixmap_handle);
   if (!pixmap) {
     VLOGF(1) << "Failed importing dummy handle";
     return nullptr;