Bug 1259733 - use forward declarations for nsIDocument in a few places; r=dholbert

This is sufficient for nsCSSFrameConstructor.h's needs, and the
corresponding C++ file already includes nsIDocument.h.

dom/animation/KeyframeEffect.h

@@ -11,7 +11,6 @@
 #include "nsCSSProperty.h"
 #include "nsCSSValue.h"
 #include "nsCycleCollectionParticipant.h"
-#include "nsIDocument.h"
 #include "nsTArray.h"
 #include "nsWrapperCache.h"
 #include "mozilla/AnimationPerformanceWarning.h"

layout/base/MobileViewportManager.cpp

@@ -14,6 +14,7 @@
 #include "nsViewManager.h"
 #include "nsViewportInfo.h"
 #include "UnitTransforms.h"
+#include "nsIDocument.h"
 
 #define MVM_LOG(...)
 // #define MVM_LOG(...) printf_stderr("MVM: " __VA_ARGS__)

layout/base/MobileViewportManager.h

@@ -8,7 +8,6 @@
 
 #include "mozilla/Maybe.h"
 #include "nsIDOMEventListener.h"
-#include "nsIDocument.h"
 #include "nsIObserver.h"
 #include "Units.h"
 

layout/base/ZoomConstraintsClient.h

@@ -9,7 +9,6 @@
 #include "FrameMetrics.h"
 #include "mozilla/Maybe.h"
 #include "nsIDOMEventListener.h"
-#include "nsIDocument.h"
 #include "nsIObserver.h"
 #include "nsWeakPtr.h"
 

layout/base/nsCSSFrameConstructor.h

@@ -20,7 +20,6 @@
 #include "nsCounterManager.h"
 #include "nsIAnonymousContentCreator.h"
 #include "nsFrameManager.h"
-#include "nsIDocument.h"
 #include "ScrollbarStyles.h"
 
 struct nsFrameItems;
@@ -31,6 +30,7 @@ struct nsGenConInitializer;
 class nsContainerFrame;
 class nsFirstLineFrame;
 class nsICSSAnonBoxPseudo;
+class nsIDocument;
 class nsPageContentFrame;
 struct PendingBinding;
 class nsGenericDOMDataNode;