macOS: Fix undesirable switch to discrete GPU during startup (issue #2398)

patch/patch.cfg

@@ -353,4 +353,9 @@ patches = [
     # https://bugs.chromium.org/p/chromium/issues/detail?id=781966
     'name': 'webkit_pointer_event_781966',
   },
+  {
+    # macOS: Fix undesirable switch to discrete GPU during startup.
+    # https://bitbucket.org/chromiumembedded/cef/issues/2398
+    'name': 'mac_gpu_2398',
+  },
 ]

patch/patches/mac_gpu_2398.patch

@@ -0,0 +1,18 @@
+diff --git ui/gl/init/gl_initializer_mac.cc ui/gl/init/gl_initializer_mac.cc
+index 828ce9bb0138..1301e6cc1d14 100644
+--- ui/gl/init/gl_initializer_mac.cc
++++ ui/gl/init/gl_initializer_mac.cc
+@@ -40,11 +40,8 @@ bool InitializeOneOffForSandbox() {
+   // GPU-related stuff is very slow without this, probably because
+   // the sandbox prevents loading graphics drivers or some such.
+   std::vector<CGLPixelFormatAttribute> attribs;
+-  if (GLContext::SwitchableGPUsSupported()) {
+-    // Avoid switching to the discrete GPU just for this pixel
+-    // format selection.
+-    attribs.push_back(kCGLPFAAllowOfflineRenderers);
+-  }
++  // Avoid switching to the discrete GPU just for this pixel format selection.
++  attribs.push_back(kCGLPFAAllowOfflineRenderers);
+   if (GetGLImplementation() == kGLImplementationAppleGL) {
+     attribs.push_back(kCGLPFARendererID);
+     attribs.push_back(