blink: Use OpenGL to flip WebGL buffer

GL_FRAMEBUFFER_FLIP_Y_MESA will tell OpenGL
to render the image upside down.  Passing
the buffer along like this will allow
ChromeOS to scan out directly from the buffer.

BUG=680851

Change-Id: I142cec041358af17652f7314ac89e82678b78d3b
Reviewed-on: https://chromium-review.googlesource.com/1117365Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Commit-Queue: Fritz Koenig <frkoenig@chromium.org>
Cr-Commit-Position: refs/heads/master@{#577396}

gpu/ipc/common/gpu_command_buffer_traits_multi.h

@@ -149,6 +149,7 @@ IPC_STRUCT_TRAITS_BEGIN(gpu::Capabilities)
   IPC_STRUCT_TRAITS_MEMBER(context_supports_distance_field_text)
   IPC_STRUCT_TRAITS_MEMBER(glyph_cache_max_texture_bytes)
   IPC_STRUCT_TRAITS_MEMBER(chromium_nonblocking_readback)
+  IPC_STRUCT_TRAITS_MEMBER(mesa_framebuffer_flip_y)
 
   IPC_STRUCT_TRAITS_MEMBER(major_version)
   IPC_STRUCT_TRAITS_MEMBER(minor_version)

third_party/blink/renderer/platform/graphics/gpu/drawing_buffer.cc

@@ -180,7 +180,9 @@ DrawingBuffer::DrawingBuffer(
       sampler_color_space_(color_params.GetSamplerGfxColorSpace()),
       use_half_float_storage_(color_params.PixelFormat() ==
                               kF16CanvasPixelFormat),
-      chromium_image_usage_(chromium_image_usage) {
+      chromium_image_usage_(chromium_image_usage),
+      opengl_flip_y_extension_(
+          ContextProvider()->GetCapabilities().mesa_framebuffer_flip_y) {
   // Used by browser tests to detect the use of a DrawingBuffer.
   TRACE_EVENT_INSTANT0("test_gpu", "DrawingBufferCreation",
                        TRACE_EVENT_SCOPE_GLOBAL);
@@ -804,10 +806,15 @@ bool DrawingBuffer::Initialize(const IntSize& size, bool use_multisampling) {
   state_restorer_->SetFramebufferBindingDirty();
   gl_->GenFramebuffers(1, &fbo_);
   gl_->BindFramebuffer(GL_FRAMEBUFFER, fbo_);
+  if (opengl_flip_y_extension_)
+    gl_->FramebufferParameteri(GL_FRAMEBUFFER, GL_FRAMEBUFFER_FLIP_Y_MESA, 1);
+
   if (WantExplicitResolve()) {
     gl_->GenFramebuffers(1, &multisample_fbo_);
     gl_->BindFramebuffer(GL_FRAMEBUFFER, multisample_fbo_);
     gl_->GenRenderbuffers(1, &multisample_renderbuffer_);
+    if (opengl_flip_y_extension_)
+      gl_->FramebufferParameteri(GL_FRAMEBUFFER, GL_FRAMEBUFFER_FLIP_Y_MESA, 1);
   }
   if (!ResizeFramebufferInternal(size)) {
     DLOG(ERROR) << "Initialization failed to allocate backbuffer.";
@@ -926,6 +933,9 @@ cc::Layer* DrawingBuffer::CcLayer() {
                                   premultiplied_alpha_false_texture_);
     layer_->SetNearestNeighbor(filter_quality_ == kNone_SkFilterQuality);
 
+    if (opengl_flip_y_extension_)
+      layer_->SetFlipped(false);
+
     GraphicsLayer::RegisterContentsLayer(layer_.get());
   }
 

third_party/blink/renderer/platform/graphics/gpu/drawing_buffer.h

@@ -591,6 +591,8 @@ class PLATFORM_EXPORT DrawingBuffer : public cc::TextureLayerClient,
   ChromiumImageUsage chromium_image_usage_;
   bool ShouldUseChromiumImage();
 
+  bool opengl_flip_y_extension_;
+
   // A release callback that is run when the previouis image passed to
   // OffscreenCanvas::Commit() is no longer needed.
   std::unique_ptr<viz::SingleReleaseCallback> previous_image_release_callback_;