Expose if we are using swiftshader via WebGraphicsContext3DProvider.

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

Index: third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.cpp
diff --git a/third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.cpp b/third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.cpp
index fb9d15055f47824ddf74d15eba03ed5fbcce659a..8a9cb40d3039de88b719622d9ab30eeb170686ea 100644
--- a/third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.cpp
+++ b/third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.cpp
@@ -154,6 +154,7 @@ DrawingBuffer::DrawingBuffer(
     , m_discardFramebufferSupported(discardFramebufferSupported)
     , m_wantAlphaChannel(wantAlphaChannel)
     , m_premultipliedAlpha(premultipliedAlpha)
+    , m_softwareRendering(m_contextProvider->isSoftwareRendering())
     , m_wantDepth(wantDepth)
     , m_wantStencil(wantStencil)
 {
@@ -276,6 +277,12 @@ bool DrawingBuffer::PrepareTextureMailbox(cc::TextureMailbox* outMailbox,
     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)
@@ -285,7 +292,7 @@ bool DrawingBuffer::PrepareTextureMailbox(cc::TextureMailbox* outMailbox,
     if (m_antiAliasingMode != None)
         commit();
 
-    if (useSharedMemory) {
+    if (m_softwareRendering) {
         std::unique_ptr<cc::SharedBitmap> bitmap = createOrRecycleBitmap();
         if (!bitmap)
             return false;