Add GLFW (DEPS-based) to third_party (#225)

GLFW is needed for the GLFW-based Windows and Linux desktop Flutter
shells.

build/secondary/third_party/glfw/BUILD.gn

@@ -0,0 +1,79 @@
+# Copyright 2013 The Flutter Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+_checkout_dir = "//third_party/glfw"
+
+config("relative_glfw_headers") {
+  include_dirs = [ "$_checkout_dir/include" ]
+}
+
+source_set("glfw") {
+  public = [
+    "$_checkout_dir/include/GLFW/glfw3.h",
+    "$_checkout_dir/include/GLFW/glfw3native.h",
+  ]
+
+  sources = [
+    "$_checkout_dir/src/context.c",
+    "$_checkout_dir/src/init.c",
+    "$_checkout_dir/src/input.c",
+    "$_checkout_dir/src/monitor.c",
+    "$_checkout_dir/src/vulkan.c",
+    "$_checkout_dir/src/window.c",
+  ]
+
+  include_dirs = [
+    "$_checkout_dir/src",
+  ]
+
+  public_configs = [
+    ":relative_glfw_headers",
+  ]
+
+  if (is_win) {
+    sources += [
+      "$_checkout_dir/src/egl_context.c",
+      "$_checkout_dir/src/egl_context.h",
+      "$_checkout_dir/src/wgl_context.c",
+      "$_checkout_dir/src/wgl_context.h",
+      "$_checkout_dir/src/win32_init.c",
+      "$_checkout_dir/src/win32_joystick.c",
+      "$_checkout_dir/src/win32_joystick.h",
+      "$_checkout_dir/src/win32_monitor.c",
+      "$_checkout_dir/src/win32_platform.h",
+      "$_checkout_dir/src/win32_time.c",
+      "$_checkout_dir/src/win32_tls.c",
+      "$_checkout_dir/src/win32_window.c",
+    ]
+
+    defines = [ "_GLFW_WIN32" ]
+  } else if (is_linux) {
+    sources += [
+      "$_checkout_dir/src/egl_context.c",
+      "$_checkout_dir/src/egl_context.h",
+      "$_checkout_dir/src/glx_context.c",
+      "$_checkout_dir/src/glx_context.h",
+      "$_checkout_dir/src/linux_joystick.c",
+      "$_checkout_dir/src/linux_joystick.h",
+      "$_checkout_dir/src/posix_tls.c",
+      "$_checkout_dir/src/posix_tls.h",
+      "$_checkout_dir/src/posix_time.c",
+      "$_checkout_dir/src/posix_time.h",
+      "$_checkout_dir/src/x11_init.c",
+      "$_checkout_dir/src/x11_monitor.c",
+      "$_checkout_dir/src/x11_platform.h",
+      "$_checkout_dir/src/x11_window.c",
+      "$_checkout_dir/src/xkb_unicode.c",
+      "$_checkout_dir/src/xkb_unicode.h",
+    ]
+
+    defines = [
+      "_GLFW_X11",
+      "_GLFW_HAS_XF86VM",
+    ]
+
+    configs -= [ "//build/config/compiler:chromium_code" ]
+    configs += [ "//build/config/compiler:no_chromium_code" ]
+  }
+}

build/secondary/third_party/glfw/README

@@ -0,0 +1,13 @@
+Name: GLFW
+License: zlib/libpng (BSD-like)
+Upstream Git: https://github.com/glfw/glfw
+Version: 3.2.1
+Description:
+
+GLFW is an Open Source, multi-platform library for OpenGL, OpenGL ES and
+Vulkan development on the desktop.
+
+To update:
+- Advance the pinned hash in DEPS, which should map the repository to
+  //third_party/glfw
+- Update BUILD.gn if necessary for changes.