Let gn check verify that blink/public dependencies are sane

We can't have gn check look through all of blink because it's
a messy monolithic pile of internal dependencies, but the
public API layer has strict rules that should be enforced by
gn check.

Also removing a mojo header from a build target since it's supposedly
already in a mojo build target and listing it here as well
makes gn check unhappy.

Bug: 898837
Change-Id: Id46485ffa4ffeb0c897f6d22e684f6d45d4804e6
Reviewed-on: https://chromium-review.googlesource.com/c/1307373
Commit-Queue: Daniel Bratell <bratell@opera.com>
Reviewed-by: Scott Graham <scottmg@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#607283}

.gn

@@ -357,6 +357,8 @@ check_targets = [
   "//third_party/blanketjs/*",
 
   # "//third_party/blink/*",  # Errors: https://crbug.com/800764
+  "//third_party/blink/public/*",
+
   #"//third_party/breakpad/*",  # Small errors.
   "//third_party/boringssl/*",
   "//third_party/bouncycastle/*",

third_party/blink/public/common/BUILD.gn

@@ -78,7 +78,6 @@ source_set("headers") {
     "picture_in_picture/picture_in_picture_control_info.h",
     "privacy_preferences.h",
     "screen_orientation/web_screen_orientation_lock_type.h",
-    "screen_orientation/web_screen_orientation_mojom_traits.h",
     "screen_orientation/web_screen_orientation_type.h",
     "service_worker/service_worker_status_code.h",
     "service_worker/service_worker_type_converters.h",