vaapi: minor style cleanup of inner classes

This CL updates code in a few locations in vaapi_decode_accelerator.cc:
- inlines the ctor and emtpy destructor of Vaapi{H264,VP8,VP9}Picture
 because, since they're in a .cc file anyway, separating declaration
 and definition is unnecessary.
- makes some members const in VaapiDecodeSurface.
- makes ctors explicit and uses scoped_refptr (and not const&), see
[1] and the discussion in [2]:

"If the function (at least sometimes) takes a ref on a refcounted
object, declare the param as scoped_refptr<T>. The caller can
decide whether it wishes to transfer ownership (by calling
std::move(t) when passing t) or retain its ref (by simply passing
t directly)."
"A great deal of Chromium code predates the above rules. In
particular, some functions take ownership of params passed as T*,
or take const scoped_refptr<T>& instead of T*, [...]. Try to clean
up such code when you find it"

[1] https://chromium.googlesource.com/chromium/src/+/master/styleguide/c++/c++.md#object-ownership-and-calling-conventions
[2] https://groups.google.com/a/chromium.org/forum/#!topic/chromium-dev/TlL1D-Djta0

TEST= **No new code intended**. Compiled simplechrome and
loaded on Soraka, then played videos making sure (via
chrome://media-internals) that GpuVideoDecoder was used.


Bug: 717265
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: I6006fb23325d23841c8613fa41d65f8707a5446c
Reviewed-on: https://chromium-review.googlesource.com/746369Reviewed-by: Kuang-che Wu <kcwu@chromium.org>
Commit-Queue: Miguel Casas <mcasas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#513108}

media/gpu/vaapi_video_decode_accelerator.cc

@@ -95,8 +95,8 @@ class VaapiVideoDecodeAccelerator::VaapiDecodeSurface
   friend class base::RefCountedThreadSafe<VaapiDecodeSurface>;
   ~VaapiDecodeSurface();
 
-  int32_t bitstream_id_;
-  scoped_refptr<VASurface> va_surface_;
+  const int32_t bitstream_id_;
+  const scoped_refptr<VASurface> va_surface_;
   gfx::Rect visible_rect_;
 };
 
@@ -109,9 +109,9 @@ VaapiVideoDecodeAccelerator::VaapiDecodeSurface::~VaapiDecodeSurface() {}
 
 class VaapiH264Picture : public H264Picture {
  public:
-  VaapiH264Picture(
-      const scoped_refptr<VaapiVideoDecodeAccelerator::VaapiDecodeSurface>&
-          dec_surface);
+  explicit VaapiH264Picture(
+      scoped_refptr<VaapiVideoDecodeAccelerator::VaapiDecodeSurface> surface)
+      : dec_surface_(surface) {}
 
   VaapiH264Picture* AsVaapiH264Picture() override { return this; }
   scoped_refptr<VaapiVideoDecodeAccelerator::VaapiDecodeSurface> dec_surface() {
@@ -119,20 +119,13 @@ class VaapiH264Picture : public H264Picture {
   }
 
  private:
-  ~VaapiH264Picture() override;
+  ~VaapiH264Picture() override {}
 
   scoped_refptr<VaapiVideoDecodeAccelerator::VaapiDecodeSurface> dec_surface_;
 
   DISALLOW_COPY_AND_ASSIGN(VaapiH264Picture);
 };
 
-VaapiH264Picture::VaapiH264Picture(
-    const scoped_refptr<VaapiVideoDecodeAccelerator::VaapiDecodeSurface>&
-        dec_surface)
-    : dec_surface_(dec_surface) {}
-
-VaapiH264Picture::~VaapiH264Picture() {}
-
 class VaapiVideoDecodeAccelerator::VaapiH264Accelerator
     : public H264Decoder::H264Accelerator {
  public:
@@ -181,9 +174,9 @@ class VaapiVideoDecodeAccelerator::VaapiH264Accelerator
 
 class VaapiVP8Picture : public VP8Picture {
  public:
-  VaapiVP8Picture(
-      const scoped_refptr<VaapiVideoDecodeAccelerator::VaapiDecodeSurface>&
-          dec_surface);
+  explicit VaapiVP8Picture(
+      scoped_refptr<VaapiVideoDecodeAccelerator::VaapiDecodeSurface> surface)
+      : dec_surface_(surface) {}
 
   VaapiVP8Picture* AsVaapiVP8Picture() override { return this; }
   scoped_refptr<VaapiVideoDecodeAccelerator::VaapiDecodeSurface> dec_surface() {
@@ -191,20 +184,13 @@ class VaapiVP8Picture : public VP8Picture {
   }
 
  private:
-  ~VaapiVP8Picture() override;
+  ~VaapiVP8Picture() override {}
 
   scoped_refptr<VaapiVideoDecodeAccelerator::VaapiDecodeSurface> dec_surface_;
 
   DISALLOW_COPY_AND_ASSIGN(VaapiVP8Picture);
 };
 
-VaapiVP8Picture::VaapiVP8Picture(
-    const scoped_refptr<VaapiVideoDecodeAccelerator::VaapiDecodeSurface>&
-        dec_surface)
-    : dec_surface_(dec_surface) {}
-
-VaapiVP8Picture::~VaapiVP8Picture() {}
-
 class VaapiVideoDecodeAccelerator::VaapiVP8Accelerator
     : public VP8Decoder::VP8Accelerator {
  public:
@@ -235,9 +221,9 @@ class VaapiVideoDecodeAccelerator::VaapiVP8Accelerator
 
 class VaapiVP9Picture : public VP9Picture {
  public:
-  VaapiVP9Picture(
-      const scoped_refptr<VaapiVideoDecodeAccelerator::VaapiDecodeSurface>&
-          dec_surface);
+  explicit VaapiVP9Picture(
+      scoped_refptr<VaapiVideoDecodeAccelerator::VaapiDecodeSurface> surface)
+      : dec_surface_(surface) {}
 
   VaapiVP9Picture* AsVaapiVP9Picture() override { return this; }
   scoped_refptr<VaapiVideoDecodeAccelerator::VaapiDecodeSurface> dec_surface() {
@@ -245,20 +231,13 @@ class VaapiVP9Picture : public VP9Picture {
   }
 
  private:
-  ~VaapiVP9Picture() override;
+  ~VaapiVP9Picture() override {}
 
   scoped_refptr<VaapiVideoDecodeAccelerator::VaapiDecodeSurface> dec_surface_;
 
   DISALLOW_COPY_AND_ASSIGN(VaapiVP9Picture);
 };
 
-VaapiVP9Picture::VaapiVP9Picture(
-    const scoped_refptr<VaapiVideoDecodeAccelerator::VaapiDecodeSurface>&
-        dec_surface)
-    : dec_surface_(dec_surface) {}
-
-VaapiVP9Picture::~VaapiVP9Picture() {}
-
 class VaapiVideoDecodeAccelerator::VaapiVP9Accelerator
     : public VP9Decoder::VP9Accelerator {
  public:
@@ -293,6 +272,7 @@ class VaapiVideoDecodeAccelerator::VaapiVP9Accelerator
 };
 
 VaapiVideoDecodeAccelerator::InputBuffer::InputBuffer() = default;
+
 VaapiVideoDecodeAccelerator::InputBuffer::~InputBuffer() = default;
 
 void VaapiVideoDecodeAccelerator::NotifyError(Error error) {
@@ -1194,7 +1174,7 @@ VaapiVideoDecodeAccelerator::VaapiH264Accelerator::CreateH264Picture() {
   if (!va_surface)
     return nullptr;
 
-  return new VaapiH264Picture(va_surface);
+  return new VaapiH264Picture(std::move(va_surface));
 }
 
 // Fill |va_pic| with default/neutral values.
@@ -1527,7 +1507,7 @@ VaapiVideoDecodeAccelerator::VaapiVP8Accelerator::CreateVP8Picture() {
   if (!va_surface)
     return nullptr;
 
-  return new VaapiVP8Picture(va_surface);
+  return new VaapiVP8Picture(std::move(va_surface));
 }
 
 #define ARRAY_MEMCPY_CHECKED(to, from)                               \
@@ -1756,7 +1736,7 @@ VaapiVideoDecodeAccelerator::VaapiVP9Accelerator::CreateVP9Picture() {
   if (!va_surface)
     return nullptr;
 
-  return new VaapiVP9Picture(va_surface);
+  return new VaapiVP9Picture(std::move(va_surface));
 }
 
 bool VaapiVideoDecodeAccelerator::VaapiVP9Accelerator::SubmitDecode(