Enable the OpenGL/WGL backend on Windows.

BUILD.gn

@@ -153,6 +153,7 @@ angle_enable_gl = false
 if (is_win) {
   angle_enable_d3d9 = true
   angle_enable_d3d11 = true
+  angle_enable_gl = true
 
   import("//build/config/win/visual_studio_version.gni")
   copy("copy_compiler_dll") {

generate_winrt_projects.py

@@ -26,6 +26,7 @@ def generateProjects(generation_dir, build_winphone):
     gyp_cmd += ' -D angle_build_winrt=1'
     gyp_cmd += ' -D angle_build_winphone=' + ('1' if build_winphone else '0')
     gyp_cmd += ' -D angle_enable_d3d9=0'
+    gyp_cmd += ' -D angle_enable_gl=0'
     gyp_cmd += ' -D angle_standalone=1'
     gyp_cmd += ' ' + os.path.join(script_dir, 'all.gyp')
 

src/angle.gyp

@@ -20,6 +20,7 @@
         [
             ['OS=="win"',
             {
+                'angle_enable_gl%': 1,
                 'angle_enable_d3d9%': 1,
                 'angle_enable_d3d11%': 1,
             }],