ui: Rename gfx::BufferUsage enum values and add BufferUsage::GPU_READ.

The problem with the current usage modes is that we currently use
SCANOUT for anything that doesn't require CPU access. When importing
a buffer we typically don't care about anything but having the GPU
be able to read from it. SCANOUT is not a good description of that
and currently means GPU read/write support.

This patch attempts to make usage more explicit and it solves the
use case where a buffer type can only provide GPU read and not GPU
write support (e.g. SHM fallback). Here are the new usage modes:

- GPU_READ
- GPU_READ_WRITE
- GPU_READ_CPU_READ_WRITE

GPU_READ is useful when importing a buffer and all you care about is
being able to use it for sampling and optionally scanout.

GPU_READ_WRITE is useful for things like WebGL or GPU raster where
we want the ability to write to the buffer using GL and potentially
use it for scanout.

GPU_READ_CPU_READ_WRITE is the usage mode that allows CPU access and
is used for one-copy and zero-copy texture initialization. There's
nothing preventing this mode from also supporting scanout.

- GPU_READ_CPU_READ_WRITE_PERSISTENT

This usage mode indicates that the data will be persistent across
Unmap()/Map() calls but will likely become part of the normal
GPU_READ_CPU_READ_WRITE usage once all buffer types support this.

BUG=538325
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel

Review URL: https://codereview.chromium.org/1420923005

Cr-Commit-Position: refs/heads/master@{#356108}

1 files changed, 0 insertions, 4 deletions

diff --git a/gpu/command_buffer/service/image_factory.h b/gpu/command_buffer/service/image_factory.h
index c805db0..3746d56 100644
--- a/gpu/command_buffer/service/image_factory.h
+++ b/gpu/command_buffer/service/image_factory.h
@@ -26,10 +26,6 @@ class GPU_EXPORT ImageFactory {
   static gfx::BufferFormat DefaultBufferFormatForImageFormat(
       unsigned internalformat);
 
-  // Returns a valid GpuMemoryBuffer usage given a valid usage as defined by
-  // CHROMIUM_gpu_memory_buffer_image.
-  static gfx::BufferUsage ImageUsageToGpuMemoryBufferUsage(unsigned usage);
-
   // Returns true if |internalformat| is compatible with |format|.
   static bool IsImageFormatCompatibleWithGpuMemoryBufferFormat(
       unsigned internalformat,