gl_surface_egl: ensure off and on screen surfaces use the same EGLConfig

ui/gl/gl_surface_egl.cc

Index: ui/gl/gl_surface_egl.cc
diff --git a/ui/gl/gl_surface_egl.cc b/ui/gl/gl_surface_egl.cc
index 7c36984843a7eadbf12da2bf7c3ec969542a492e..fc18978989f6f3508c6772f439f6a75a1b8cafa6 100644
--- a/ui/gl/gl_surface_egl.cc
+++ b/ui/gl/gl_surface_egl.cc
@@ -35,6 +35,10 @@ extern "C" {
 #include "ui/ozone/public/surface_factory_ozone.h"
 #endif
 
+#if defined(USE_X11) && !defined(OS_CHROMEOS)
+#include "ui/gfx/x/x11_switches.h"
+#endif
+
 #if !defined(EGL_FIXED_SIZE_ANGLE)
 #define EGL_FIXED_SIZE_ANGLE 0x3201
 #endif
@@ -273,9 +277,21 @@ bool GLSurfaceEGL::InitializeOneOff() {
           switches::kEnableUnsafeES3APIs)) {
     renderable_type = EGL_OPENGL_ES3_BIT;
   }
+
+  EGLint buffer_size = 32;
+  EGLint alpha_size = 8;
+
+#if defined(USE_X11) && !defined(OS_CHROMEOS)
+  if (!base::CommandLine::ForCurrentProcess()->HasSwitch(
+          switches::kEnableTransparentVisuals)) {

[piman, 2015/11/17 20:53:52]

I would prefer if we didn't rely on behavior of the browser side relative to
this flag ("if that flag is set, then the browser must have created windows with
32 bit visuals otherwise it must be 24 bits"). I think we should solve the
problem the same way we solved it for GLX, i.e. by using an unmapped window
rather than a pbuffer, and getting a config that's compatible with it.

In the long run, I think what we really need to do is pick a visual in the
browser (early enough), pass that to the GPU process, and pick a config out of
that.

+    buffer_size = 24;
+    alpha_size = 0;
+  }
+#endif
+
   const EGLint kConfigAttribs[] = {
-    EGL_BUFFER_SIZE, 32,
-    EGL_ALPHA_SIZE, 8,
+    EGL_BUFFER_SIZE, buffer_size,
+    EGL_ALPHA_SIZE, alpha_size,
     EGL_BLUE_SIZE, 8,
     EGL_GREEN_SIZE, 8,
     EGL_RED_SIZE, 8,