Use float for scroll offset.

third_party/WebKit/Source/platform/scroll/ScrollTypes.h

Index: third_party/WebKit/Source/platform/scroll/ScrollTypes.h
diff --git a/third_party/WebKit/Source/platform/scroll/ScrollTypes.h b/third_party/WebKit/Source/platform/scroll/ScrollTypes.h
index cf6930baca7d512cf22a42e4c9a8437eb9a8b9f8..aed3a91d00a2af42be89c4c0efc3a5c2ebba2b38 100644
--- a/third_party/WebKit/Source/platform/scroll/ScrollTypes.h
+++ b/third_party/WebKit/Source/platform/scroll/ScrollTypes.h
@@ -26,11 +26,18 @@
 #ifndef ScrollTypes_h
 #define ScrollTypes_h
 
-#include "platform/geometry/FloatSize.h"
+#include "platform/geometry/FloatPoint.h"
 #include "wtf/Assertions.h"
 
 namespace blink {
 
+typedef float ScrollUnit;

[skobes, 2016/10/05 21:19:28]

I'm not sure we get much value from this.  Even if we convert everything now I
think we will accumulate an arbitrary mix of ScrollUnit and bare float over
time.

[szager1, 2016/10/06 00:11:57]

Yeah, I tend to agree.  I'll back this bit out and leave it for a follow-up that
may never happen.

+typedef FloatSize ScrollOffset;

[skobes, 2016/10/05 21:19:28]

Let's add a comment here about what ScrollOffset means.  (Can be a pointer to
the README.)

[szager1, 2016/10/06 00:11:57]

Done.

+
+inline ScrollOffset toScrollOffset(const FloatPoint& p) {
+  return ScrollOffset(p.x(), p.y());
+}
+
 enum ScrollDirection {
   ScrollUpIgnoringWritingMode,
   ScrollDownIgnoringWritingMode,
@@ -214,17 +221,18 @@ struct ScrollResult {
   float unusedScrollDeltaY;
 };
 
-inline FloatSize toScrollDelta(ScrollbarOrientation orientation, float delta) {
-  return orientation == HorizontalScrollbar ? FloatSize(delta, 0.0f)
-                                            : FloatSize(0.0f, delta);
+inline ScrollOffset toScrollDelta(ScrollbarOrientation orientation,
+                                  float delta) {
+  return orientation == HorizontalScrollbar ? ScrollOffset(delta, 0.0f)
+                                            : ScrollOffset(0.0f, delta);
 }
 
-inline FloatSize toScrollDelta(ScrollDirectionPhysical dir, float delta) {
+inline ScrollOffset toScrollDelta(ScrollDirectionPhysical dir, float delta) {
   if (dir == ScrollUp || dir == ScrollLeft)
     delta = -delta;
 
-  return (dir == ScrollLeft || dir == ScrollRight) ? FloatSize(delta, 0)
-                                                   : FloatSize(0, delta);
+  return (dir == ScrollLeft || dir == ScrollRight) ? ScrollOffset(delta, 0)
+                                                   : ScrollOffset(0, delta);
 }
 
 typedef unsigned ScrollbarControlPartMask;