Fix content_browser_client breaks by forward declaring blink::mojom types

Removes /third_party/blink/public/mojom/ #includes from
/content/public/browser/content_browser_client.h.  Instead, forward
declares blink::mojom types.  This fixes sporadic build breaks where
unluckly builds fail to find generated headers like
/third_party/blink/public/mojom/badging/badging.mojom-forward.h

Bug: 1049216
Change-Id: I8df7bf9d12797917f4aa9b3b0193e76317965229
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2041033Reviewed-by: Matt Falkenhagen <falken@chromium.org>
Commit-Queue: Steve Becker <stevebe@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#738877}

content/public/browser/content_browser_client.h

@@ -44,9 +44,6 @@
 #include "services/network/public/mojom/websocket.mojom-forward.h"
 #include "storage/browser/file_system/file_system_context.h"
 #include "third_party/blink/public/common/user_agent/user_agent_metadata.h"
-#include "third_party/blink/public/mojom/badging/badging.mojom-forward.h"
-#include "third_party/blink/public/mojom/credentialmanager/credential_manager.mojom-forward.h"
-#include "third_party/blink/public/mojom/web_feature/web_feature.mojom-forward.h"
 #include "ui/accessibility/ax_mode.h"
 #include "ui/base/page_transition_types.h"
 #include "ui/base/window_open_disposition.h"
@@ -83,10 +80,13 @@ class SequencedTaskRunner;
 
 namespace blink {
 namespace mojom {
+class BadgeService;
+class CredentialManager;
 class RendererPreferences;
 class RendererPreferenceWatcher;
 class WebUsbService;
 class WindowFeatures;
+enum class WebFeature : int32_t;
 }  // namespace mojom
 class AssociatedInterfaceRegistry;
 class URLLoaderThrottle;