Add CRWWebViewScrollViewProxy.dragging which will be used in

CWVScrollView.

BUG=714543

Review-Url: https://codereview.chromium.org/2840013004
Cr-Commit-Position: refs/heads/master@{#467560}

ios/web/public/web_state/ui/crw_web_view_scroll_view_proxy.h

@@ -24,6 +24,7 @@
 @interface CRWWebViewScrollViewProxy : NSObject<UIScrollViewDelegate>
 @property(nonatomic, assign) CGPoint contentOffset;
 @property(nonatomic, assign) UIEdgeInsets contentInset;
+@property(nonatomic, readonly, getter=isDragging) BOOL dragging;
 @property(nonatomic, readonly) BOOL isZooming;
 @property(nonatomic, readonly) CGFloat zoomScale;
 @property(nonatomic, assign) UIEdgeInsets scrollIndicatorInsets;

ios/web/web_state/ui/crw_web_view_scroll_view_proxy.mm

@@ -93,6 +93,10 @@
   [_scrollView setBounces:bounces];
 }
 
+- (BOOL)isDragging {
+  return [_scrollView isDragging];
+}
+
 - (BOOL)isZooming {
   return [_scrollView isZooming];
 }

ios/web/web_state/ui/crw_web_view_scroll_view_proxy_unittest.mm

@@ -101,6 +101,12 @@ TEST_F(CRWWebViewScrollViewProxyTest, testScrollViewPresent) {
   [[[mockScrollView_ stub] andReturnValue:[NSValue valueWithCGRect:frame]]
       frame];
   EXPECT_TRUE(CGRectEqualToRect(frame, [webViewScrollViewProxy_ frame]));
+
+  [[[mockScrollView_ expect] andReturnValue:@YES] isDragging];
+  EXPECT_TRUE([webViewScrollViewProxy_ isDragging]);
+
+  [[[mockScrollView_ expect] andReturnValue:@NO] isDragging];
+  EXPECT_FALSE([webViewScrollViewProxy_ isDragging]);
 }
 
 // Tests that CRWWebViewScrollViewProxy returns the correct property values when
@@ -117,6 +123,7 @@ TEST_F(CRWWebViewScrollViewProxyTest, testScrollViewAbsent) {
   EXPECT_TRUE(
       CGSizeEqualToSize(CGSizeZero, [webViewScrollViewProxy_ contentSize]));
   EXPECT_TRUE(CGRectEqualToRect(CGRectZero, [webViewScrollViewProxy_ frame]));
+  EXPECT_FALSE([webViewScrollViewProxy_ isDragging]);
 
   // Make sure setting the properties is fine too.
   // Arbitrary point.