mac: Only let two-finger-scrolling trigger history if web doesn't swallow gesture

chrome/browser/renderer_host/render_widget_host_view_mac.h

Index: chrome/browser/renderer_host/render_widget_host_view_mac.h
diff --git a/chrome/browser/renderer_host/render_widget_host_view_mac.h b/chrome/browser/renderer_host/render_widget_host_view_mac.h
index 42e295d638e22587622c51dae39a820faee89e71..ef35e314def9711adda1bab1875c92838a7237f6 100644
--- a/chrome/browser/renderer_host/render_widget_host_view_mac.h
+++ b/chrome/browser/renderer_host/render_widget_host_view_mac.h
@@ -117,9 +117,32 @@ class RWHVMEditCommandHelper;
 
   // Whether the previous mouse event was ignored due to hitTest check.
   BOOL mouseEventWasIgnored_;
+
+  // If a scroll event came back unhandled from the renderer. Set to |NO| at
+  // the start of a scroll gesture, and then to |YES| if a scroll event comes
+  // back unhandled from the renderer.
+  // Used for history swiping.
+  BOOL gotUnhandledWheelEvent_;
+
+  // Cummulative scroll delta since scroll gesture start. Only valid during
+  // scroll gesture handling. Used for history swiping.
+  NSSize totalScrollDelta_;
+
+  // If the viewport is scrolled all the way to the left or right.
+  // Used for history swiping.
+  BOOL isPinnedLeft_;
+  BOOL isPinnedRight_;
+
+  // If the main frame has a horizontal scrollbar.
+  // Used for history swiping.
+  BOOL hasHorizontalScrollbar_;
 }
 
 @property(nonatomic, readonly) NSRange selectedRange;
+@property(nonatomic) BOOL gotUnhandledWheelEvent;
+@property(nonatomic, setter=setPinnedLeft:) BOOL isPinnedLeft;
+@property(nonatomic, setter=setPinnedRight:) BOOL isPinnedRight;
+@property(nonatomic) BOOL hasHorizontalScrollbar;
 
 - (void)setCanBeKeyView:(BOOL)can;
 - (void)setTakesFocusOnlyOnMouseDown:(BOOL)b;
@@ -280,6 +303,13 @@ class RenderWidgetHostViewMac : public RenderWidgetHostView {
 
   virtual void SetVisuallyDeemphasized(const SkColor* color, bool animate);
 
+  virtual void UnhandledWheelEvent(
+      const WebKit::WebMouseWheelEvent& event) OVERRIDE;
+  virtual void SetHasHorizontalScrollbar(
+      bool has_horizontal_scrollbar) OVERRIDE;
+  virtual void SetScrollOffsetPinning(
+      bool is_pinned_to_left, bool is_pinned_to_right) OVERRIDE;
+
   void KillSelf();
 
   void SetTextInputActive(bool active);