Add stubs for A4A opt-in library.

BUILD.gn

@@ -223,6 +223,33 @@ static_library("angle_image_util") {
   ]
 }
 
+config("angle_feature_support_util_config") {
+  include_dirs = [
+    "include",
+    "src",
+  ]
+  defines = [ "LIBANGLE_UTIL_IMPLEMENTATION" ]
+}
+
+static_library("angle_feature_support_util") {
+  sources = [
+    "src/feature_support_util/feature_support_util.cpp",
+    "src/feature_support_util/feature_support_util.h",
+  ]
+
+  configs -= angle_undefine_configs
+  configs += [
+    ":internal_config",
+    ":extra_warnings",
+  ]
+
+  public_configs = [ ":angle_feature_support_util_config" ]
+
+  public_deps = [
+    ":angle_common",
+  ]
+}
+
 config("angle_gpu_info_util_config") {
   include_dirs = [
     "include",
@@ -466,6 +493,7 @@ static_library("libANGLE") {
     ":angle_common",
   ]
   deps = [
+    ":angle_feature_support_util",
     ":angle_gpu_info_util",
     ":angle_image_util",
     ":commit_id",

src/feature_support_util/feature_support_util.cpp

+//
+// Copyright 2018 The ANGLE Project Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+//
+
+// feature_support_util.cpp: Implementation of the code that helps the Android EGL loader
+// determine whether to use ANGLE or a native GLES driver.
+
+#include "feature_support_util.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+ANGLE_EXPORT bool ANGLEUseForApplication(const char *appName,
+                                         const char *deviceMfr,
+                                         const char *deviceModel,
+                                         ANGLEPreference developerOption,
+                                         ANGLEPreference appPreference)
+{
+    if (developerOption != ANGLE_NO_PREFERENCE)
+    {
+        return (developerOption == ANGLE_PREFER_ANGLE);
+    }
+    else if ((appPreference != ANGLE_NO_PREFERENCE) && false /*rules allow app to choose*/)
+    {
+        return (appPreference == ANGLE_PREFER_ANGLE);
+    }
+    else
+    {
+        return false /*whatever the rules come up with*/;
+    }
+}
+
+#ifdef __cplusplus
+}  // extern "C"
+#endif

src/feature_support_util/feature_support_util.h

+//
+// Copyright 2018 The ANGLE Project Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+//
+
+// feature_support_util.cpp: Helps Android EGL loader to determine whether to use ANGLE or a native
+// GLES driver.  Can be extended in the future for more-general feature selection.
+
+#ifndef FEATURE_SUPPORT_UTIL_H_
+#define FEATURE_SUPPORT_UTIL_H_
+
+#include "export.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+// TODO(ianelliott@google.com angleproject:2801): Revisit this enum.  Make it
+// strongly typed, and look at renaming it and its values.
+typedef enum ANGLEPreference {
+    ANGLE_NO_PREFERENCE = 0,
+    ANGLE_PREFER_NATIVE = 1,
+    ANGLE_PREFER_ANGLE  = 2,
+} ANGLEPreference;
+
+// TODO(ianelliott@google.com angleproject:2801): Revisit this function
+// name/interface.  Look at generalizing it and making it more "feature"
+// oriented.
+ANGLE_EXPORT bool ANGLEUseForApplication(const char *appName,
+                                         const char *deviceMfr,
+                                         const char *deviceModel,
+                                         ANGLEPreference developerOption,
+                                         ANGLEPreference appPreference);
+
+#ifdef __cplusplus
+}  // extern "C"
+#endif
+
+#endif  // FEATURE_SUPPORT_UTIL_H_