chrome: Cleanup class/struct forward declarations

chrome/browser/gpu/gpu_feature_checker.h

Index: chrome/browser/gpu/gpu_feature_checker.h
diff --git a/chrome/browser/gpu/gpu_feature_checker.h b/chrome/browser/gpu/gpu_feature_checker.h
index 873ca41493712c76a6be24b33f7da637643b195c..1e45a92b0e5fc30b4cda941661be04d4fc98c444 100644
--- a/chrome/browser/gpu/gpu_feature_checker.h
+++ b/chrome/browser/gpu/gpu_feature_checker.h
@@ -11,10 +11,6 @@
 #include "content/public/browser/gpu_data_manager_observer.h"
 #include "gpu/config/gpu_feature_type.h"
 
-namespace content {
-class GpuDataManager;
-}  // namespace content
-
 class GPUFeatureChecker : public base::RefCountedThreadSafe<GPUFeatureChecker>,
                           public content::GpuDataManagerObserver {
  public: