[fuchsia] Fix Chromium build.

For some unknown reason, during the Chromium build, the
third_party/dawn/third_party:glfw always get rebuilt even when
nothing actually references is (as is the case for "is_fuchsia ==
true").

This ends up in a build failure, since glfw doesn't support this
platform. See [1] for an example.

This CL is a work-around that makes the library empty for Fuchsia
instead. Note that this is never linked into anything so should
not be an issue for any Chromium-related code either.

[1] https://chromium-review.googlesource.com/c/chromium/src/+/1795302

Bug=dawn:221

Change-Id: Ia4344e93b01722b3dd0cddf70a5d13a5b71488b7
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/11041
Commit-Queue: David Turner <digit@google.com>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
diff --git a/third_party/BUILD.gn b/third_party/BUILD.gn
index 4a52372..53e56db 100644
--- a/third_party/BUILD.gn
+++ b/third_party/BUILD.gn
@@ -265,21 +265,26 @@
     ]
   }
 
-  sources = [
-    "${glfw_dir}/include/GLFW/glfw3.h",
-    "${glfw_dir}/include/GLFW/glfw3native.h",
-    "${glfw_dir}/src/context.c",
-    "${glfw_dir}/src/egl_context.c",
-    "${glfw_dir}/src/egl_context.h",
-    "${glfw_dir}/src/init.c",
-    "${glfw_dir}/src/input.c",
-    "${glfw_dir}/src/internal.h",
-    "${glfw_dir}/src/monitor.c",
-    "${glfw_dir}/src/osmesa_context.c",
-    "${glfw_dir}/src/osmesa_context.h",
-    "${glfw_dir}/src/vulkan.c",
-    "${glfw_dir}/src/window.c",
-  ]
+  # NOTE: For some unknown reason, this library gets build when is_fuchsia
+  # is true, even if absolutely nothing references it, as checked with
+  # `gn refs out/Fuchsia third_party/dawn/third_party:glfw --all`
+  if (!is_fuchsia) {
+    sources = [
+      "${glfw_dir}/include/GLFW/glfw3.h",
+      "${glfw_dir}/include/GLFW/glfw3native.h",
+      "${glfw_dir}/src/context.c",
+      "${glfw_dir}/src/egl_context.c",
+      "${glfw_dir}/src/egl_context.h",
+      "${glfw_dir}/src/init.c",
+      "${glfw_dir}/src/input.c",
+      "${glfw_dir}/src/internal.h",
+      "${glfw_dir}/src/monitor.c",
+      "${glfw_dir}/src/osmesa_context.c",
+      "${glfw_dir}/src/osmesa_context.h",
+      "${glfw_dir}/src/vulkan.c",
+      "${glfw_dir}/src/window.c",
+    ]
+  }
   libs = []
 
   if (is_win) {