Remove unused mask and background methods.

Bumped into these methods while investigating background layers. They were
not in use.

Review URL: https://codereview.chromium.org/310623002

git-svn-id: svn://svn.chromium.org/blink/trunk@175275 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/core/rendering/style/RenderStyle.h

@@ -1132,9 +1132,6 @@ public:
     void setWordSpacing(float);
     void setLetterSpacing(float);
 
-    void clearBackgroundLayers() { m_background.access()->m_background = FillLayer(BackgroundFillLayer); }
-    void inheritBackgroundLayers(const FillLayer& parent) { m_background.access()->m_background = parent; }
-
     void adjustBackgroundLayers()
     {
         if (backgroundLayers()->next()) {
@@ -1143,9 +1140,6 @@ public:
         }
     }
 
-    void clearMaskLayers() { rareNonInheritedData.access()->m_mask = FillLayer(MaskFillLayer); }
-    void inheritMaskLayers(const FillLayer& parent) { rareNonInheritedData.access()->m_mask = parent; }
-
     void adjustMaskLayers()
     {
         if (maskLayers()->next()) {