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 90 matching lines @@
         return std::move(recycled.bitmap);
     }
 
     return Platform::current()->allocateSharedBitmap(m_size);
 }
 
 bool DrawingBuffer::PrepareTextureMailbox(cc::TextureMailbox* outMailbox,
     std::unique_ptr<cc::SingleReleaseCallback>* outReleaseCallback,
     bool useSharedMemory)
 {
+    bool forceGpuResult = false;
+    return prepareTextureMailboxInternal(outMailbox, outReleaseCallback, forceGpuResult);
+}
+
+bool DrawingBuffer::prepareTextureMailboxInternal(

[danakj, 2016/08/22 22:57:44]

I added a prepareTextureMailboxInternal that lets the caller force a gpu mailbox
result even under swiftshader, for the transferToStaticBitmapImage to use.

+    cc::TextureMailbox* outMailbox,
+    std::unique_ptr<cc::SingleReleaseCallback>* outReleaseCallback,
+    bool forceGpuResult)
+{
     if (m_destructionInProgress) {
         // It can be hit in the following sequence.
         // 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 && !forceGpuResult) {
         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 99 matching lines @@
     m_recycledBitmapQueue.append(std::move(recycled));
 }
 
 PassRefPtr<StaticBitmapImage> DrawingBuffer::transferToStaticBitmapImage()
 {
     // This can be null if the context is lost before the first call to grContext().
     GrContext* grContext = m_contextProvider->grContext();
 
     cc::TextureMailbox textureMailbox;
     std::unique_ptr<cc::SingleReleaseCallback> releaseCallback;
-    bool useSharedMemory = false;
     bool success = false;
-    if (grContext)
-        success = PrepareTextureMailbox(&textureMailbox, &releaseCallback, useSharedMemory);
+    if (grContext) {
+        bool forceGpuResult = true;
+        success = prepareTextureMailboxInternal(&textureMailbox, &releaseCallback, forceGpuResult);
+    }
     if (!success) {
         // If we can't get a mailbox, return an transparent black ImageBitmap.
         // The only situation this could happen is when two or more calls to transferToImageBitmap are made back-to-back, or when the context gets lost.
         sk_sp<SkSurface> surface = SkSurface::MakeRasterN32Premul(m_size.width(), m_size.height());
         return StaticBitmapImage::create(fromSkSp(surface->makeImageSnapshot()));
     }
 
     DCHECK_EQ(m_size.width(), textureMailbox.size_in_pixels().width());
     DCHECK_EQ(m_size.height(), textureMailbox.size_in_pixels().height());
 
@@ skipping 791 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