ui: Make gfx::Size::Scale() mutate the class. Add gfx::ScaleSize() similar to Rect/Point.

cc/page_scale_animation.cc

 // Copyright 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "config.h"
 
 #include "cc/page_scale_animation.h"
 
 #include "cc/geometry.h"
 #include "ui/gfx/point_f.h"
@@ skipping 83 matching lines @@
     // the target scale is impossible to attain without hitting the root layer
     // edges, then infer an anchor that doesn't collide with the edges.
     // We will interpolate between the two anchors during the animation.
     inferTargetScrollOffsetFromStartAnchor();
     clampTargetScrollOffset();
     inferTargetAnchorFromScrollOffsets();
 }
 
 gfx::SizeF PageScaleAnimation::viewportSizeAtScale(float pageScaleFactor) const
 {
-    return gfx::SizeF(m_viewportSize.width() / pageScaleFactor, m_viewportSize.height() / pageScaleFactor);
+    return gfx::ScaleSize(m_viewportSize, 1 / pageScaleFactor);
 }
 
 void PageScaleAnimation::inferTargetScrollOffsetFromStartAnchor()
 {
     gfx::Vector2dF anchorRelativeToStartViewport = m_startAnchor - m_startScrollOffset;
     gfx::Vector2dF normalized = normalizeFromViewport(anchorRelativeToStartViewport, viewportSizeAtScale(m_startPageScaleFactor));
     m_targetScrollOffset = m_startAnchor - denormalizeToViewport(normalized, viewportSizeAtScale(m_targetPageScaleFactor));
 }
 
 void PageScaleAnimation::inferTargetAnchorFromScrollOffsets()
@@ skipping 89 matching lines @@
 
     // Linearly interpolate the magnitude in log scale.
     float diff = m_targetPageScaleFactor / m_startPageScaleFactor;
     float logDiff = log(diff);
     logDiff *= interp;
     diff = exp(logDiff);
     return m_startPageScaleFactor * diff;
 }
 
 }  // namespace cc