Add half-float IOSurface GpuMemoryBuffer support

gpu/command_buffer/common/gpu_memory_buffer_support.cc

Index: gpu/command_buffer/common/gpu_memory_buffer_support.cc
diff --git a/gpu/command_buffer/common/gpu_memory_buffer_support.cc b/gpu/command_buffer/common/gpu_memory_buffer_support.cc
index 68237a08fd255e6ffc020f530493d662ffad0290..a78499ff701b053c1a460f70a5a7082a1e8063ee 100644
--- a/gpu/command_buffer/common/gpu_memory_buffer_support.cc
+++ b/gpu/command_buffer/common/gpu_memory_buffer_support.cc
@@ -84,6 +84,7 @@ bool IsImageFormatCompatibleWithGpuMemoryBufferFormat(
     case gfx::BufferFormat::RGBX_8888:
       return internalformat == GL_RGB;
     case gfx::BufferFormat::RGBA_4444:
+    case gfx::BufferFormat::RGBA_F16:
       return internalformat == GL_RGBA;
   }
 
@@ -115,6 +116,8 @@ bool IsGpuMemoryBufferFormatSupported(gfx::BufferFormat format,
     case gfx::BufferFormat::RGBA_4444:
     case gfx::BufferFormat::RGBA_8888:
     case gfx::BufferFormat::RGBX_8888:
+    case gfx::BufferFormat::RGBA_F16:
+      return capabilities.texture_half_float_linear;

[Daniele Castagna, 2017/03/30 21:47:10]

Does this return false on all the non-mac platforms?
Does having support for texture_half_float_linear means we can also allocate
Gmbs with that format?

What if we're allocating shmem GMBs?

[ccameron, 2017/03/30 23:07:03]

Ops, this affected the behavior of the above cases. Fixed that.

IIUC this returns true if we can texture out of this GMB type, which should be
okay for any platform (even the ones where we can't create native half-float
GMBs).

But I may not understand the function's purpose completely.

[Daniele Castagna, 2017/03/31 00:25:20]

Looking at IsGpuMemoryBufferFormatSupported makes me think this returning true
means we can allocate a GBM with that format.

For gfx::BufferFormat::UYVY_422 for example, image_ycbcr_422 is true only on
mac:
https://cs.chromium.org/chromium/src/gpu/command_buffer/service/feature_info....

Should this return false on all the platforms where we can't allocate a RGBA_F16
GMB?

     case gfx::BufferFormat::YVU_420:
       return true;
     case gfx::BufferFormat::YUV_420_BIPLANAR:
@@ -150,6 +153,7 @@ bool IsImageSizeValidForGpuMemoryBufferFormat(const gfx::Size& size,
     case gfx::BufferFormat::RGBX_8888:
     case gfx::BufferFormat::BGRA_8888:
     case gfx::BufferFormat::BGRX_8888:
+    case gfx::BufferFormat::RGBA_F16:
       return true;
     case gfx::BufferFormat::YVU_420:
     case gfx::BufferFormat::YUV_420_BIPLANAR: