Expand is_linux to is_linux || is_chromeos.

Currently is_linux GN variable is set to true on Chrome OS build,
but is is planned to set false. This is the preparation to
keep the compatibility.

Bug: chromium:1110266
Test: Built locally.
Change-Id: I87e8f1312c85f85a3f882698f1dce3d65e0cfab6
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/48348
Kokoro-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Tested-by: Hidehiko Abe <hidehiko@google.com>

src/Vulkan/BUILD.gn

diff --git a/src/Vulkan/BUILD.gn b/src/Vulkan/BUILD.gn
index c3f503b..a8d0765 100644
--- a/src/Vulkan/BUILD.gn
+++ b/src/Vulkan/BUILD.gn
@@ -18,7 +18,7 @@
 
 # Need a separate config to ensure the warnings are added to the end.
 config("swiftshader_libvulkan_private_config") {
-  if (is_linux) {
+  if (is_linux || is_chromeos) {
     defines = [
       "VK_USE_PLATFORM_XLIB_KHR",
       "VK_USE_PLATFORM_XCB_KHR",
@@ -96,7 +96,7 @@
     "VkStringify.hpp",
     "VulkanPlatform.hpp",
   ]
-  if (is_linux || is_android) {
+  if (is_linux || is_chromeos || is_android) {
     sources += [
       "VkDeviceMemoryExternalLinux.hpp",
       "VkSemaphoreExternalLinux.hpp",
@@ -161,7 +161,7 @@
       "-Wl,-exported_symbols_list," +
           rebase_path("vk_swiftshader.exports", root_build_dir),
     ]
-  } else if (is_linux || is_fuchsia) {
+  } else if (is_linux || is_chromeos || is_fuchsia) {
     inputs = [
       "vk_swiftshader.lds",
     ]