fix d3d ext float blend

Bug: chromium:930993, chromium:938602
Change-Id: Ie2e07369eca663b1507c7811a1a06ce5efc892ee
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1516007
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>

src/libANGLE/renderer/d3d/d3d11/renderer11_utils.cpp

@@ -1609,6 +1609,8 @@ void GenerateCaps(ID3D11Device *device,
     // and https://msdn.microsoft.com/en-us/library/windows/desktop/ff476900(v=vs.85).aspx
     extensions->robustBufferAccessBehavior = true;
     extensions->blendMinMax                = true;
+    // https://docs.microsoft.com/en-us/windows/desktop/direct3ddxgi/format-support-for-direct3d-11-0-feature-level-hardware
+    extensions->floatBlend                 = true;
     extensions->framebufferBlit            = GetFramebufferBlitSupport(featureLevel);
     extensions->framebufferMultisample     = GetFramebufferMultisampleSupport(featureLevel);
     extensions->instancedArraysANGLE       = GetInstancingSupport(featureLevel);

src/libANGLE/renderer/d3d/d3d9/renderer9_utils.cpp

@@ -709,6 +709,8 @@ void GenerateCaps(IDirect3D9 *d3d9,
     // https://www.khronos.org/registry/OpenGL/extensions/ARB/ARB_robustness.txt
     extensions->robustBufferAccessBehavior = false;
     extensions->blendMinMax                = true;
+    // https://docs.microsoft.com/en-us/windows/desktop/direct3ddxgi/format-support-for-direct3d-feature-level-9-1-hardware
+    extensions->floatBlend                 = false;
     extensions->framebufferBlit            = true;
     extensions->framebufferMultisample     = true;
     extensions->instancedArraysANGLE       = deviceCaps.PixelShaderVersion >= D3DPS_VERSION(3, 0);