Full Screen Magnifier: Prevent the unintentional zoom origin drift on unzooming.

This fixes the unintentional zoom origin drift described at http://crbug.com/160472.

Major changes:
- Update the formula of calculate new position in RedrawKeepingMousePosition()
- Use the float instead of integer in calculation of the position.
- Add the float version of ConvertPointToDIP() in dip_util.cc

BUG=160472
TEST=manual

Review URL: https://chromiumcodereview.appspot.com/11348059

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@169454 0039d316-1c4b-4281-b951-d872f2087c98

2 files changed, 9 insertions, 0 deletions

diff --git a/ui/compositor/dip_util.cc b/ui/compositor/dip_util.cc
index 104a5da..1f6309a 100644
--- a/ui/compositor/dip_util.cc
+++ b/ui/compositor/dip_util.cc
@@ -29,6 +29,11 @@ gfx::Point ConvertPointToDIP(const Layer* layer,
       gfx::ScalePoint(point_in_pixel, 1.0f / GetDeviceScaleFactor(layer)));
 }
 
+gfx::PointF ConvertPointToDIP(const Layer* layer,
+                              const gfx::PointF& point_in_pixel) {
+  return gfx::ScalePoint(point_in_pixel, 1.0f / GetDeviceScaleFactor(layer));
+}
+
 gfx::Size ConvertSizeToDIP(const Layer* layer,
                            const gfx::Size& size_in_pixel) {
   return gfx::ToFlooredSize(
diff --git a/ui/compositor/dip_util.h b/ui/compositor/dip_util.h
index d793dc7..e8d0367 100644
--- a/ui/compositor/dip_util.h
+++ b/ui/compositor/dip_util.h
@@ -7,6 +7,7 @@
 
 #include "ui/compositor/compositor_export.h"
 #include "base/basictypes.h"
+#include "ui/gfx/point_f.h"
 
 namespace gfx {
 class Point;
@@ -24,6 +25,9 @@ COMPOSITOR_EXPORT float GetDeviceScaleFactor(const Layer* layer);
 COMPOSITOR_EXPORT gfx::Point ConvertPointToDIP(
     const Layer* layer,
     const gfx::Point& point_in_pixel);
+COMPOSITOR_EXPORT gfx::PointF ConvertPointToDIP(
+    const Layer* layer,
+    const gfx::PointF& point_in_pixel);
 COMPOSITOR_EXPORT gfx::Size ConvertSizeToDIP(
     const Layer* layer,
     const gfx::Size& size_in_pixel);