CCing hubbe@ that worked on half-float support in video frames.

dshwang@chromium.org (works at Intel) is currently investigating if using RG_88 to represent 16 bits of precision, and using customized shaders to read out the values is reasonable. If RG_88 turns out to be efficient, then half-floats will not be needed. As a bonus, we already have RG_88 buffers, and they have much wider support than half-floats.

See here: https://codereview.chromium.org/2122573003/

I suspect that skia wants 4 high-accuracy channels per shader (RGBA), which is a little trickier to implement by using two 8-bit channels for each 16-bit value, but *could* be implemented by using MRT.

dshwang@chromium.org also claims that GpuMemoryBuffer cannot support LUMINANCE_F16, for some reason related to linux kernel support, not sure what he means by that exactly, I might be able to find his argument somewhere.

GL_LUMINANCE_F16 has been replaced by GL_R16F. Hardware also supports GL_R16 (as a unorm).

If this isn't supported in the kernel yet, the fix is to add support in the kernel.

Mac has support for these formats as IOSurfaces.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/c1fcde58c22a5825c44cbad17eb3ed84b8c2bcce

commit c1fcde58c22a5825c44cbad17eb3ed84b8c2bcce
Author: ccameron <ccameron@chromium.org>
Date: Wed Apr 12 19:47:00 2017

Add half-float IOSurface GpuMemoryBuffer support

Add support for gpu rasterization to half-float RGBA textures.

Do not add software rasterization support for half-float RGBA textures.
While this is possible, software rasterization to half-float is not a good
idea for performance reasons.

BUG= 655171 
CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_trusty_blink_rel;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

Review-Url: https://codereview.chromium.org/2786103003
Cr-Commit-Position: refs/heads/master@{#464114}

[modify] https://crrev.com/c1fcde58c22a5825c44cbad17eb3ed84b8c2bcce/cc/raster/raster_buffer_provider.cc
[modify] https://crrev.com/c1fcde58c22a5825c44cbad17eb3ed84b8c2bcce/cc/resources/resource_format.cc
[modify] https://crrev.com/c1fcde58c22a5825c44cbad17eb3ed84b8c2bcce/cc/resources/resource_provider.cc
[modify] https://crrev.com/c1fcde58c22a5825c44cbad17eb3ed84b8c2bcce/components/exo/buffer.cc
[modify] https://crrev.com/c1fcde58c22a5825c44cbad17eb3ed84b8c2bcce/content/browser/gpu/gpu_internals_ui.cc
[modify] https://crrev.com/c1fcde58c22a5825c44cbad17eb3ed84b8c2bcce/gpu/command_buffer/common/gpu_memory_buffer_support.cc
[modify] https://crrev.com/c1fcde58c22a5825c44cbad17eb3ed84b8c2bcce/gpu/command_buffer/common/gpu_memory_buffer_support.h
[modify] https://crrev.com/c1fcde58c22a5825c44cbad17eb3ed84b8c2bcce/gpu/command_buffer/tests/gl_gpu_memory_buffer_unittest.cc
[modify] https://crrev.com/c1fcde58c22a5825c44cbad17eb3ed84b8c2bcce/gpu/ipc/client/command_buffer_proxy_impl.cc
[modify] https://crrev.com/c1fcde58c22a5825c44cbad17eb3ed84b8c2bcce/gpu/ipc/client/gpu_memory_buffer_impl_shared_memory.cc
[modify] https://crrev.com/c1fcde58c22a5825c44cbad17eb3ed84b8c2bcce/gpu/ipc/common/gpu_memory_buffer_support.cc
[modify] https://crrev.com/c1fcde58c22a5825c44cbad17eb3ed84b8c2bcce/gpu/ipc/host/gpu_memory_buffer_support.cc
[modify] https://crrev.com/c1fcde58c22a5825c44cbad17eb3ed84b8c2bcce/gpu/ipc/in_process_command_buffer.cc
[modify] https://crrev.com/c1fcde58c22a5825c44cbad17eb3ed84b8c2bcce/gpu/ipc/service/gpu_command_buffer_stub.cc
[modify] https://crrev.com/c1fcde58c22a5825c44cbad17eb3ed84b8c2bcce/ui/gfx/buffer_format_util.cc
[modify] https://crrev.com/c1fcde58c22a5825c44cbad17eb3ed84b8c2bcce/ui/gfx/buffer_types.h
[modify] https://crrev.com/c1fcde58c22a5825c44cbad17eb3ed84b8c2bcce/ui/gfx/mac/io_surface.cc
[modify] https://crrev.com/c1fcde58c22a5825c44cbad17eb3ed84b8c2bcce/ui/gfx/mojo/buffer_types.mojom
[modify] https://crrev.com/c1fcde58c22a5825c44cbad17eb3ed84b8c2bcce/ui/gfx/mojo/buffer_types_struct_traits.h
[modify] https://crrev.com/c1fcde58c22a5825c44cbad17eb3ed84b8c2bcce/ui/gl/gl_image_io_surface.mm
[modify] https://crrev.com/c1fcde58c22a5825c44cbad17eb3ed84b8c2bcce/ui/gl/gl_image_io_surface_unittest.cc
[modify] https://crrev.com/c1fcde58c22a5825c44cbad17eb3ed84b8c2bcce/ui/gl/gl_image_memory.cc
[modify] https://crrev.com/c1fcde58c22a5825c44cbad17eb3ed84b8c2bcce/ui/gl/gl_image_native_pixmap.cc
[modify] https://crrev.com/c1fcde58c22a5825c44cbad17eb3ed84b8c2bcce/ui/gl/test/gl_image_test_support.cc

Removing the sRGB part (new bug) and closing (half-float is in).