Expose if we are using swiftshader via WebGraphicsContext3DProvider.

third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.cpp

 /*
  * Copyright (c) 2010, Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 136 matching lines @@
     bool wantDepth,
     bool wantStencil)
     : m_preserveDrawingBuffer(preserve)
     , m_webGLVersion(webGLVersion)
     , m_contextProvider(std::move(contextProvider))
     , m_gl(m_contextProvider->contextGL())
     , m_extensionsUtil(std::move(extensionsUtil))
     , m_discardFramebufferSupported(discardFramebufferSupported)
     , m_wantAlphaChannel(wantAlphaChannel)
     , m_premultipliedAlpha(premultipliedAlpha)
+    , m_softwareRendering(m_contextProvider->isSoftwareRendering())
     , m_wantDepth(wantDepth)
     , m_wantStencil(wantStencil)
 {
     memset(m_colorMask, 0, 4 * sizeof(GLboolean));
     memset(m_clearColor, 0, 4 * sizeof(GLfloat));
     // Used by browser tests to detect the use of a DrawingBuffer.
     TRACE_EVENT_INSTANT0("test_gpu", "DrawingBufferCreation", TRACE_EVENT_SCOPE_GLOBAL);
 }
 
 DrawingBuffer::~DrawingBuffer()
@@ skipping 102 matching lines @@
         // 1. WebGL draws something.
         // 2. The compositor begins the frame.
         // 3. Javascript makes a context lost using WEBGL_lose_context extension.
         // 4. Here.
         return false;
     }
     ASSERT(!m_isHidden);
     if (!m_contentsChanged)
         return false;
 
+    // If the context is lost, we don't know if we should be producing GPU or
+    // software frames, until we get a new context, since the compositor will
+    // be trying to get a new context and may change modes.
+    if (m_gl->GetGraphicsResetStatusKHR() != GL_NO_ERROR)
+        return false;
+
     TRACE_EVENT0("blink,rail", "DrawingBuffer::prepareMailbox");
 
     if (m_newMailboxCallback)
         (*m_newMailboxCallback)();
 
     // Resolve the multisampled buffer into m_colorBuffer texture.
     if (m_antiAliasingMode != None)
         commit();
 
-    if (useSharedMemory) {
+    if (m_softwareRendering) {
         std::unique_ptr<cc::SharedBitmap> bitmap = createOrRecycleBitmap();
         if (!bitmap)
             return false;
         unsigned char* pixels = bitmap->pixels();
         DCHECK(pixels);
 
         bool needPremultiply = m_wantAlphaChannel && !m_premultipliedAlpha;
         WebGLImageConversion::AlphaOp op = needPremultiply ? WebGLImageConversion::AlphaDoPremultiply : WebGLImageConversion::AlphaDoNothing;
         readBackFramebuffer(pixels, size().width(), size().height(), ReadbackSkia, op);
 
@@ skipping 914 matching lines @@
 
 void DrawingBuffer::restoreTextureBindings()
 {
     // This class potentially modifies the bindings for GL_TEXTURE_2D and
     // GL_TEXTURE_RECTANGLE. Only GL_TEXTURE_2D needs to be restored since
     // the public interface for WebGL does not support GL_TEXTURE_RECTANGLE.
     m_gl->BindTexture(GL_TEXTURE_2D, m_texture2DBinding);
 }
 
 } // namespace blink