Support offscreen contexts which own their backing surface

content/renderer/renderer_blink_platform_impl.cc

Index: content/renderer/renderer_blink_platform_impl.cc
diff --git a/content/renderer/renderer_blink_platform_impl.cc b/content/renderer/renderer_blink_platform_impl.cc
index b267bdba1ce0be729373a7b86a9d650a22d388ce..d3e0fb4f2e7b03c4ae014035f50a7a11a5fc50ef 100644
--- a/content/renderer/renderer_blink_platform_impl.cc
+++ b/content/renderer/renderer_blink_platform_impl.cc
@@ -1017,17 +1017,28 @@ RendererBlinkPlatformImpl::createOffscreenGraphicsContext3DProvider(
   // This is an offscreen context, which doesn't use the default frame buffer,
   // so don't request any alpha, depth, stencil, antialiasing.
   gpu::gles2::ContextCreationAttribHelper attributes;
-  attributes.alpha_size = -1;
-  attributes.depth_size = 0;
-  attributes.stencil_size = 0;
-  attributes.samples = 0;
-  attributes.sample_buffers = 0;
+
+  if (web_attributes.supportOwnOffscreenSurface) {

[aelias_OOO_until_Jul13, 2017/02/16 03:25:51]

It doesn't look like this outer if statement is needed because the ternary
operator on each individual attribute covers it, so please remove it.

[klausw, 2017/02/16 20:06:57]

Done, and also updated the comment above to match the new behavior.

+    attributes.own_offscreen_surface = true;
+    attributes.alpha_size = web_attributes.supportAlpha ? 8 : -1;
+    attributes.depth_size = web_attributes.supportDepth ? 24 : 0;
+    attributes.stencil_size = web_attributes.supportStencil ? 8 : 0;
+    attributes.samples = web_attributes.supportAntialias ? 4 : 0;
+    attributes.sample_buffers = 0;
+  } else {
+    attributes.alpha_size = -1;
+    attributes.depth_size = 0;
+    attributes.stencil_size = 0;
+    attributes.samples = 0;
+    attributes.sample_buffers = 0;
+  }
   attributes.bind_generates_resource = false;
   // Prefer discrete GPU for WebGL.
   attributes.gpu_preference = gl::PreferDiscreteGpu;
 
   attributes.fail_if_major_perf_caveat =
       web_attributes.failIfMajorPerformanceCaveat;
+

[aelias_OOO_until_Jul13, 2017/02/16 03:25:51]

nit: unnecessary newline

[klausw, 2017/02/16 20:06:57]

Done.

   DCHECK_GT(web_attributes.webGLVersion, 0u);
   DCHECK_LE(web_attributes.webGLVersion, 2u);
   if (web_attributes.webGLVersion == 2)