Convert test dep to use dawn_angle_dir

This CL updates the dep in the dawn test to use the `${dawn_angle_dir}`
instead of `//third_party/angle` to match other gn files.

Bug: dawn:1372
Change-Id: I5ac5b39e3ca98e8061eb5ae3cd757841c8711bbd
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/86862
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Auto-Submit: Dan Sinclair <dsinclair@chromium.org>
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Stephen White <senorblanco@google.com>
Commit-Queue: Stephen White <senorblanco@google.com>

src/dawn/tests/BUILD.gn

@@ -555,9 +555,9 @@ source_set("white_box_tests_sources") {
     deps += [ "${dawn_root}/src/dawn/utils:glfw" ]
   }
 
-  if (dawn_enable_opengles) {
+  if (dawn_enable_opengles && defined(dawn_angle_dir)) {
     sources += [ "white_box/EGLImageWrappingTests.cpp" ]
-    deps += [ "//third_party/angle:libEGL" ]
+    deps += [ "${dawn_angle_dir}:libEGL" ]
   }
 
   libs = []