Remove SupportsDXGI1_2 and Supporting Code

Per Microsoft docs, IDXGIAdapter2 will always be present on >= Win8
machines.

Since Chromium and ANGLE only support >= Win10, we no longer need to
track and report this histogram.

Bug: chromium:475877310
Change-Id: Iba82ecd9c8ea7a406f3f8de6511da932c1607eee
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/7487704
Commit-Queue: Rafael Cintron <rafael.cintron@microsoft.com>
Reviewed-by: Geoff Lang <geofflang@chromium.org>

Author: RafaelCintron

src/libANGLE/renderer/d3d/d3d11/Renderer11.cpp

@@ -436,7 +436,6 @@ Renderer11::Renderer11(egl::Display *display)
     mRenderer11DeviceCaps.supportsClearView                      = false;
     mRenderer11DeviceCaps.supportsConstantBufferOffsets          = false;
     mRenderer11DeviceCaps.supportsVpRtIndexWriteFromVertexShader = false;
-    mRenderer11DeviceCaps.supportsDXGI1_2                        = false;
     mRenderer11DeviceCaps.allowES3OnFL10_0                       = false;
     mRenderer11DeviceCaps.supportsTypedUAVLoadAdditionalFormats  = false;
     mRenderer11DeviceCaps.supportsUAVLoadStoreCommonFormats      = false;
@@ -1112,9 +1111,6 @@ egl::Error Renderer11::initializeDevice()
     ASSERT(!mPixelTransfer);
     mPixelTransfer = new PixelTransfer11(this);
 
-    // Gather stats on DXGI and D3D feature level
-    ANGLE_HISTOGRAM_BOOLEAN("GPU.ANGLE.SupportsDXGI1_2", mRenderer11DeviceCaps.supportsDXGI1_2);
-
     ANGLEFeatureLevel angleFeatureLevel = GetANGLEFeatureLevel(mRenderer11DeviceCaps.featureLevel);
 
     // We don't actually request a 11_1 device, because of complications with the platform
@@ -1231,10 +1227,6 @@ void Renderer11::populateRenderer11DeviceCaps()
     PopulateFormatDeviceCaps(mDevice.Get(), DXGI_FORMAT_B5G5R5A1_UNORM,
                              &mRenderer11DeviceCaps.B5G5R5A1support,
                              &mRenderer11DeviceCaps.B5G5R5A1maxSamples);
-
-    angle::ComPtr<IDXGIAdapter2> dxgiAdapter2;
-    mDxgiAdapter.As(&dxgiAdapter2);
-    mRenderer11DeviceCaps.supportsDXGI1_2 = (dxgiAdapter2 != nullptr);
 }
 
 gl::SupportedSampleSet Renderer11::generateSampleSetForEGLConfig(
@@ -1434,8 +1426,7 @@ void Renderer11::generateDisplayExtensions(egl::DisplayExtensions *outExtensions
     // If present path fast is active then the surface orientation extension isn't supported
     outExtensions->surfaceOrientation = !mPresentPathFastEnabled;
 
-    // D3D11 does not support present with dirty rectangles until DXGI 1.2.
-    outExtensions->postSubBuffer = mRenderer11DeviceCaps.supportsDXGI1_2;
+    outExtensions->postSubBuffer = true;
 
     outExtensions->image                 = true;
     outExtensions->imageBase             = true;

src/libANGLE/renderer/d3d/d3d11/Renderer11.h

@@ -49,7 +49,6 @@ struct Renderer11DeviceCaps
     Renderer11DeviceCaps();
 
     D3D_FEATURE_LEVEL featureLevel;
-    bool supportsDXGI1_2;                         // Support for DXGI 1.2
     bool supportsClearView;                       // Support for ID3D11DeviceContext1::ClearView
     bool supportsConstantBufferOffsets;           // Support for Constant buffer offset
     bool supportsVpRtIndexWriteFromVertexShader;  // VP/RT can be selected in the Vertex Shader

src/libANGLE/renderer/d3d/d3d11/SwapChain11.cpp

@@ -654,10 +654,7 @@ EGLint SwapChain11::reset(DisplayD3D *displayD3D,
             }
         }
 
-        if (mRenderer->getRenderer11DeviceCaps().supportsDXGI1_2)
-        {
-            mSwapChain1 = d3d11::DynamicCastComObject<IDXGISwapChain1>(mSwapChain);
-        }
+        mSwapChain1 = d3d11::DynamicCastComObject<IDXGISwapChain1>(mSwapChain);
 
         ID3D11Texture2D *backbufferTex = nullptr;
         hr                             = mSwapChain->GetBuffer(0, __uuidof(ID3D11Texture2D),