Make sure ANGLE can find the proper libraries when running tests

This cl is in the context of replacing SwiftShader's GL libraries
with SwANGLE (ANGLE with SwiftShader Vulkan as its backend). In order
to allow ANGLE to find the proper libvulkan.so when executing tests
on the bots, we have to make sure the proper rpath is set.

This affects all tests that depend directly or indirectly on
//ui/gl:test_support.

The affected tests include:
app_shell_unittests
aura_unittests
cc_unittests
compositor_unittests
gpu_unittests
interactive_ui_tests
message_center_unittests
media_unittests
snapshot_unittests
unit_tests
views_unittests
viz_unittests
wm_unittests

Bug: chromium:1060139
Change-Id: Ida242f511599d38ad1ec16e0f4711d80a957cc8f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2565490Reviewed-by: Kenneth Russell <kbr@chromium.org>
Reviewed-by: Greg Thompson <grt@chromium.org>
Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Reviewed-by: danakj <danakj@chromium.org>
Commit-Queue: Alexis Hétu <sugoi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#833354}

content/test/BUILD.gn

@@ -387,6 +387,7 @@ static_library("test_support") {
     "//third_party/blink/public:blink",
     "//third_party/blink/public:test_support",
     "//third_party/blink/public/strings:strings_grit",
+    "//ui/gl:test_support",
   ]
 
   deps = [
@@ -459,7 +460,6 @@ static_library("test_support") {
     "//ui/events/blink",
     "//ui/gfx:test_support",
     "//ui/gl",
-    "//ui/gl:test_support",
     "//ui/native_theme",
     "//ui/resources",
     "//ui/shell_dialogs:shell_dialogs",

ui/gl/BUILD.gn

@@ -512,6 +512,15 @@ static_library("test_support") {
   if (use_ozone) {
     deps += [ "//ui/ozone" ]
   }
+
+  public_configs = []
+
+  # If the run-time search path isn't set properly when we use ANGLE with its
+  # Vulkan backend, it may end up finding the system libvulkan.so rather than
+  # the one built in the output directory
+  if ((is_linux || is_chromeos) && !is_component_build) {
+    public_configs += [ "//build/config/gcc:rpath_for_built_shared_libraries" ]
+  }
 }
 
 source_set("run_all_unittests") {