Reduce the size of execution_context.h

execution_context.h is used in 4400+ compilation units. This reduces
its pre-processed size by ~1.1M.

The referrer_policy.mojom-shared.h include was added by
https://crrev.com/611587.

Bug: 242216, 860403
Change-Id: I5cdcbf17f05a6b121672f7fa9263f098a6450ee5
Reviewed-on: https://chromium-review.googlesource.com/c/1408970
Reviewed-by: Kent Tamura <tkent@chromium.org>
Commit-Queue: Fredrik Söderquist <fs@opera.com>
Cr-Commit-Position: refs/heads/master@{#622488}
diff --git a/third_party/blink/renderer/core/execution_context/execution_context.h b/third_party/blink/renderer/core/execution_context/execution_context.h
index a77299d..d970ada 100644
--- a/third_party/blink/renderer/core/execution_context/execution_context.h
+++ b/third_party/blink/renderer/core/execution_context/execution_context.h
@@ -33,7 +33,6 @@
 #include "base/location.h"
 #include "base/macros.h"
 #include "base/unguessable_token.h"
-#include "services/network/public/mojom/referrer_policy.mojom-shared.h"
 #include "third_party/blink/renderer/bindings/core/v8/sanitize_script_errors.h"
 #include "third_party/blink/renderer/core/core_export.h"
 #include "third_party/blink/renderer/core/dom/context_lifecycle_notifier.h"
@@ -52,6 +51,12 @@
 class InterfaceProvider;
 }
 
+namespace network {
+namespace mojom {
+enum class ReferrerPolicy : int32_t;
+}  // namespace mojom
+}  // namespace network
+
 namespace blink {
 
 class ContentSecurityPolicy;