Implements core logic for Pixel Canvas

ui/views/view.h

Index: ui/views/view.h
diff --git a/ui/views/view.h b/ui/views/view.h
index dddf1590e616fb08b5bb9c3f3d6a0f841af302f2..3786b028a1690a00a41a9025257902dd25762d9f 100644
--- a/ui/views/view.h
+++ b/ui/views/view.h
@@ -1268,6 +1268,12 @@ class VIEWS_EXPORT View : public ui::LayerDelegate,
   // hierarchy).
   virtual void OnNativeThemeChanged(const ui::NativeTheme* theme) {}
 
+  // Pixel Canvas --------------------------------------------------------------
+
+  // Returns the type of scaling to be done for this View. Values should be from
+  // ui::PaintContext::ScaleType.
+  virtual int GetContextScaleType() const;

[sky, 2017/06/23 23:40:23]

Why is this virtual? Why would it need to be overriden? And why is the return
type int instead of ScaleType?

[malaykeshav, 2017/06/24 00:30:03]

The ScaleType can vary depending on whether we are scaling to fit/snap (default)
or 
if we are simply scaling with no snapping.

With scaling by fractional scale factors, the effective scale factor is
different 
from the original scale factor due to rounding. 

 - In Scale to Fit/Snap, all the draw commands are scaled via the effective
scale 
   factor.
 - But this leads to some undesired scaling in terms of images or vector icons, 
   that require consistent scaling along x and y axis. (effective scale along x 
   may not be equal to effective scale along y). For such cases we use Scale To 
   Scale Factor. Which scales all draw commands with device_scale_factor_. But
the 
   canvas is still bounded with the scale to fit bounds (For any child snapping
and
   FillCanvas() like commands).

By default this function returns SCALE_TO_FIT. In case a view wants to
SCALE_TO_SCALE_FACTOR, it can
override accordingly and return the correct enum.
This can also be made a member variable along with a setter.

I was using int as the return type to prevent including paint_context.h files in
all the header files that were overriding this function.

+
   // Debugging -----------------------------------------------------------------
 
 #if !defined(NDEBUG)
@@ -1316,12 +1322,13 @@ class VIEWS_EXPORT View : public ui::LayerDelegate,
   // during painting.
   bool ShouldPaint() const;
 
-  // Returns the offset that should be used when constructing the paint context
+  // Returns the bounds that should be used when constructing the paint context
   // for this view.
-  gfx::Vector2d GetPaintContextOffset() const;
+  gfx::Rect GetPaintContextBounds() const;
 
   // Adjusts the transform of |recorder| in advance of painting.
-  void SetupTransformRecorderForPainting(ui::TransformRecorder* recorder) const;
+  void SetupTransformRecorderForPainting(ui::TransformRecorder* recorder,
+                                         const ui::PaintContext& context) const;
 
   // Recursively calls the painting method |func| on all non-layered children,
   // in Z order.