Refactor GL surface format handling

ui/gl/init/gl_factory_win.cc

Index: ui/gl/init/gl_factory_win.cc
diff --git a/ui/gl/init/gl_factory_win.cc b/ui/gl/init/gl_factory_win.cc
index 9a43d7ad1de775d134b0a6ac111395fd92ade1a5..309b3ed308d24b930cb1f3ddcdfda7c56e1690a2 100644
--- a/ui/gl/init/gl_factory_win.cc
+++ b/ui/gl/init/gl_factory_win.cc
@@ -93,16 +93,22 @@ scoped_refptr<GLSurface> CreateViewGLSurface(gfx::AcceleratedWidget window) {
   }
 }
 
-scoped_refptr<GLSurface> CreateOffscreenGLSurface(const gfx::Size& size) {
+scoped_refptr<GLSurface> CreateOffscreenGLSurfaceWithFormat(
+    const gfx::Size& size, GLSurfaceFormat format) {
   TRACE_EVENT0("gpu", "gl::init::CreateOffscreenGLSurface");
   switch (GetGLImplementation()) {
     case kGLImplementationOSMesaGL:
-      return InitializeGLSurface(
-          new GLSurfaceOSMesa(GLSurface::SURFACE_OSMESA_RGBA, size));
+      if (format.IsDefault()) {
+        format = GLSurfaceFormat(GLSurfaceFormat::SURFACE_OSMESA_RGBA);
+      }
+      return InitializeGLSurfaceWithFormat(
+          new GLSurfaceOSMesa(format, size), format);
     case kGLImplementationEGLGLES2:
-      return InitializeGLSurface(new PbufferGLSurfaceEGL(size));
+      return InitializeGLSurfaceWithFormat(
+          new PbufferGLSurfaceEGL(size), format);
     case kGLImplementationDesktopGL:
-      return InitializeGLSurface(new PbufferGLSurfaceWGL(size));
+      return InitializeGLSurfaceWithFormat(
+          new PbufferGLSurfaceWGL(size), format);
     case kGLImplementationMockGL:
       return new GLSurfaceStub;
     default: