Viz unittest YUV fix

When an OpenGL implementation exposes the GL_OES_texture_half_float_linear
extension, the YUV format can be set to L16F. Since OSMesa doesn't
expose this extension, the test currently doesn't fail in this case, but
it fails when ran with SwiftShader. This fixes the issue.

Bug: chromium:848035
Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:mac_optional_gpu_tests_rel;luci.chromium.try:win_optional_gpu_tests_rel
Change-Id: I076ee00ba187f6d89cc51de41f15f0872d4d728c
Reviewed-on: https://chromium-review.googlesource.com/1080030Reviewed-by: danakj <danakj@chromium.org>
Reviewed-by: Fredrik Hubinette <hubbe@chromium.org>
Commit-Queue: Alexis Hétu <sugoi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#563060}

components/viz/service/display/renderer_pixeltest.cc

@@ -29,6 +29,7 @@
 #include "gpu/command_buffer/client/gles2_interface.h"
 #include "media/base/video_frame.h"
 #include "media/renderers/video_resource_updater.h"
+#include "media/video/half_float_maker.h"
 #include "third_party/skia/include/core/SkColorPriv.h"
 #include "third_party/skia/include/core/SkColorSpaceXform.h"
 #include "third_party/skia/include/core/SkMatrix.h"
@@ -446,18 +447,25 @@ void CreateTestYUVVideoDrawQuad_FromVideoFrame(
   ResourceFormat yuv_highbit_resource_format =
       video_resource_updater->YuvResourceFormat(bits_per_channel);
 
-  float multiplier = 1.0;
+  float offset = 0.0f;
+  float multiplier = 1.0f;
 
-  if (yuv_highbit_resource_format == R16_EXT)
+  if (yuv_highbit_resource_format == R16_EXT) {
     multiplier = 65535.0f / ((1 << bits_per_channel) - 1);
-  else
+  } else if (yuv_highbit_resource_format == LUMINANCE_F16) {
+    std::unique_ptr<media::HalfFloatMaker> half_float_maker =
+        media::HalfFloatMaker::NewHalfFloatMaker(bits_per_channel);
+    offset = half_float_maker->Offset();
+    multiplier = half_float_maker->Multiplier();
+  } else {
     bits_per_channel = 8;
+  }
 
   yuv_quad->SetNew(shared_state, rect, visible_rect, needs_blending,
                    ya_tex_coord_rect, uv_tex_coord_rect, ya_tex_size,
                    uv_tex_size, mapped_resource_y, mapped_resource_u,
                    mapped_resource_v, mapped_resource_a, video_color_space,
-                   0.0f, multiplier, bits_per_channel);
+                   offset, multiplier, bits_per_channel);
 }
 
 void CreateTestY16TextureDrawQuad_FromVideoFrame(