Make scroll offset type of float in cc

cc/trees/layer_tree_host.cc

Index: cc/trees/layer_tree_host.cc
diff --git a/cc/trees/layer_tree_host.cc b/cc/trees/layer_tree_host.cc
index eed1e5a7e151e74942e0b78d54b96f38a2f2874d..6a7f8a26b1c3c2d7c4879edee6d0b465c57111f2 100644
--- a/cc/trees/layer_tree_host.cc
+++ b/cc/trees/layer_tree_host.cc
@@ -40,6 +40,7 @@
 #include "cc/trees/single_thread_proxy.h"
 #include "cc/trees/thread_proxy.h"
 #include "cc/trees/tree_synchronizer.h"
+#include "ui/gfx/geometry/vector2d_conversions.h"
 #include "ui/gfx/size_conversions.h"
 
 namespace {
@@ -1066,8 +1067,8 @@ void LayerTreeHost::ApplyScrollAndScale(ScrollAndScaleSet* info) {
     QueueSwapPromise(swap_promise.Pass());
   }
 
-  gfx::Vector2d inner_viewport_scroll_delta;
-  gfx::Vector2d outer_viewport_scroll_delta;
+  gfx::Vector2dF inner_viewport_scroll_delta;
+  gfx::Vector2dF outer_viewport_scroll_delta;
 
   for (size_t i = 0; i < info->scrolls.size(); ++i) {
     Layer* layer = LayerTreeHostCommon::FindLayerInSubtree(
@@ -1079,8 +1080,9 @@ void LayerTreeHost::ApplyScrollAndScale(ScrollAndScaleSet* info) {
     } else if (layer == inner_viewport_scroll_layer_.get()) {
       inner_viewport_scroll_delta += info->scrolls[i].scroll_delta;
     } else {
-      layer->SetScrollOffsetFromImplSide(layer->scroll_offset() +
-                                         info->scrolls[i].scroll_delta);
+      layer->SetScrollOffsetFromImplSide(
+          layer->scroll_offset() +
+          gfx::ScrollOffset(info->scrolls[i].scroll_delta));
     }
   }
 
@@ -1098,18 +1100,20 @@ void LayerTreeHost::ApplyScrollAndScale(ScrollAndScaleSet* info) {
 
     inner_viewport_scroll_layer_->SetScrollOffsetFromImplSide(
         inner_viewport_scroll_layer_->scroll_offset() +
-        inner_viewport_scroll_delta);
+        gfx::ScrollOffset(inner_viewport_scroll_delta));;

[danakj, 2014/09/25 22:01:26]

double;;

[Yufeng Shen (Slow to review), 2014/09/26 20:19:07]

Done.

     if (outer_viewport_scroll_layer_.get()) {
       outer_viewport_scroll_layer_->SetScrollOffsetFromImplSide(
           outer_viewport_scroll_layer_->scroll_offset() +
-          outer_viewport_scroll_delta);
+          gfx::ScrollOffset(outer_viewport_scroll_delta));

[danakj, 2014/09/25 22:01:26]

Throwing this out as an idea, idk if it's a good one. I see lots of 

offset + gfx::ScrollOffset(delta)

we could have a

gfx::ScrollOffset ScrollOffsetWithDelta(offset, delta) that did this. It would
actually make a bit more characters at call sites, though. Would it be more
clear? What do you think?

[Yufeng Shen (Slow to review), 2014/09/25 22:15:01]

what do you think if I have an overload

ScrollOffset operator+(const ScrollOffset& lhs, const Vector2dF& rhs) ?
ScrollOffset operator+(const ScrollOffset& lhs, const Vector2d& rhs)

there are a lot of calls in the unittest files that have this 
offset + delta or offset + delta + delta pattern
having these overload will make the change much simpler.

     }
     ApplyPageScaleDeltaFromImplSide(info->page_scale_delta);
 
-    client_->ApplyViewportDeltas(
-        inner_viewport_scroll_delta + outer_viewport_scroll_delta,
-        info->page_scale_delta,
-        info->top_controls_delta);
+    gfx::Vector2dF viewport_scroll_delta =
+        inner_viewport_scroll_delta + outer_viewport_scroll_delta;
+
+    client_->ApplyViewportDeltas(gfx::ToFlooredVector2d(viewport_scroll_delta),

[danakj, 2014/09/25 22:01:26]

why flooring here? not sure why you changed anything here

[Yufeng Shen (Slow to review), 2014/09/26 20:19:07]

Done.

+                                 info->page_scale_delta,
+                                 info->top_controls_delta);
   }
 }