Set dawn_angle_dir to //third_party/angle

If this isn't set, there's no libEGL so glfwCreateWindow fails and
may sometimes kill the test bot running dawn_end2end_tests.
It's probably desirable to set `dawn_angle_dir` in Chromium builds
for WebGPU compat as well.

Bug: dawn:1375
Change-Id: I7693b7d80ca99527930dd082ed9e453d10c4b708
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3597108
Reviewed-by: Stephen White <senorblanco@chromium.org>
Reviewed-by: Bruce Dawson <brucedawson@chromium.org>
Commit-Queue: Austin Eng <enga@chromium.org>
Cr-Commit-Position: refs/heads/main@{#994903}

build_overrides/dawn.gni

@@ -3,6 +3,7 @@
 # found in the LICENSE file.
 
 # The paths to Dawn's dependencies
+dawn_angle_dir = "//third_party/angle"
 dawn_glfw_dir = "//third_party/glfw/src"
 dawn_googletest_dir = "//third_party/googletest/src"
 dawn_jinja2_dir = "//third_party/jinja2"