Update BUILD flags to support Chrome OS

This CL updates a few flags to support Chrome OS:

- Disables the OpenGL backend on Chrome OS builds.
- Removes the X11 dependency for Chrome OS builds because we do not
support X11.
- Removes the XCB dependency (again, no X11).

BUG=chromium:993457
TEST=e2e and unit tests build and pass on Intel Chrome OS devices

Change-Id: I1cb06453ccc94d1b68a6998ea635bddd6fb7b5ad
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/10100
Commit-Queue: Kai Ninomiya <kainino@chromium.org>
Reviewed-by: Austin Eng <enga@chromium.org>
Reviewed-by: Kai Ninomiya <kainino@chromium.org>

scripts/dawn_features.gni

@@ -33,7 +33,7 @@ declare_args() {
 
   # Enables the compilation of Dawn's OpenGL backend
   # (best effort, non-conformant)
-  dawn_enable_opengl = is_linux
+  dawn_enable_opengl = is_linux && !is_chromeos
 
   # Enables the compilation of Dawn's Vulkan backend
   dawn_enable_vulkan = is_linux || is_win

src/common/BUILD.gn

@@ -60,6 +60,10 @@ config("dawn_internal") {
     defines += [ "DAWN_ENABLE_BACKEND_VULKAN" ]
   }
 
+  if (is_linux && !is_chromeos) {
+    defines += [ "DAWN_USE_X11" ]
+  }
+
   # Only internal Dawn targets can use this config, this means only targets in
   # this BUILD.gn file.
   visibility = [ ":*" ]

src/common/vulkan_platform.h

@@ -157,7 +157,7 @@ class alignas(kNativeVkHandleAlignment) VkNonDispatchableHandle {
 #    include "common/windows_with_undefs.h"
 #endif
 // Remove X11/Xlib.h macros after vulkan_platform's include of it.
-#if defined(DAWN_PLATFORM_LINUX)
+#if defined(DAWN_USE_X11)
 #    include "common/xlib_with_undefs.h"
 #endif
 

third_party/BUILD.gn

@@ -122,7 +122,7 @@ config("vulkan_headers_config") {
   if (is_win) {
     defines = [ "VK_USE_PLATFORM_WIN32_KHR" ]
   }
-  if (is_linux) {
+  if (is_linux && !is_chromeos) {
     defines = [ "VK_USE_PLATFORM_XCB_KHR" ]
   }
   if (is_android) {