Add DEPS rule to prevent further dependencies on ui/accessibility/platform

Bug: 1006402
Change-Id: I2ad9f834dd69ce149528d749d7b9c4e7dfa9d988
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1826599
Commit-Queue: Dominic Mazzoni <dmazzoni@chromium.org>
Reviewed-by: Kurt Catti-Schmidt <kschmi@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#700455}

ui/accessibility/DEPS

@@ -11,6 +11,15 @@ include_rules = [
   "+ui/gfx",
   "+ui/display",
   "+ui/strings/grit/ui_strings.h",
+
+  # Don't allow dependencies from ui/accessibility on
+  # ui/accessibility/platform.
+  #
+  # The code in ui/accessibility should be safe to include from any process,
+  # on any platform. In comparison, ui/accessibility/platform is only meant
+  # to be used in the browser process on platforms with a native
+  # accessibility API.
+  "-ui/accessibility/platform",
 ]
 
 specific_include_rules = {
@@ -20,4 +29,17 @@ specific_include_rules = {
   "ax_assistant_util.h": [
     "+ui/accessibility/mojom",
   ],
+
+  # Normally we shouldn't depend on ui/accessibility/platform, but this
+  # is okay because it's just constants.
+  "ax_assistant_structure.cc": [
+    "+ui/accessibility/platform/ax_android_constants.h",
+  ],
+
+  # Normally we shouldn't depend on ui/accessibility/platform,
+  # but it's harmless for this particular test, and it's probably
+  # better to keep this test next to the code it tests.
+  "ax_range_unittest.cc": [
+    "+ui/accessibility/platform",
+  ],
 }