Mac: Enable partial swap

This is pretty trivial when using the overlay path. Just create a
new layer for the damage. The partial damage layer can be created,
removed, or resized with basically no cost, because its backing is the
already-existing IOSurface.

As each partial swap comes in, union the existing overlay layer's
rect with the rect of the new partial swap. If this grows "too big",
then do a full swap (which clears the accumulated union). The
constants here are pretty arbitrary.

BUG=474299

Review URL: https://codereview.chromium.org/1271123002

Cr-Commit-Position: refs/heads/master@{#342771}

2 files changed, 26 insertions, 0 deletions

diff --git a/ui/gfx/geometry/rect_f.cc b/ui/gfx/geometry/rect_f.cc
index c87ea3d..a15bdf3 100644
--- a/ui/gfx/geometry/rect_f.cc
+++ b/ui/gfx/geometry/rect_f.cc
@@ -6,6 +6,12 @@
 
 #include <algorithm>
 
+#if defined(OS_IOS)
+#include <CoreGraphics/CoreGraphics.h>
+#elif defined(OS_MACOSX)
+#include <ApplicationServices/ApplicationServices.h>
+#endif
+
 #include "base/logging.h"
 #include "base/strings/stringprintf.h"
 #include "ui/gfx/geometry/insets_f.h"
@@ -24,6 +30,16 @@ static void AdjustAlongAxis(float dst_origin,
     *origin = std::min(dst_origin + dst_size, *origin + *size) - *size;
 }
 
+#if defined(OS_MACOSX)
+RectF::RectF(const CGRect& r)
+    : origin_(r.origin.x, r.origin.y), size_(r.size.width, r.size.height) {
+}
+
+CGRect RectF::ToCGRect() const {
+  return CGRectMake(x(), y(), width(), height());
+}
+#endif
+
 void RectF::Inset(const InsetsF& insets) {
   Inset(insets.left(), insets.top(), insets.right(), insets.bottom());
 }
diff --git a/ui/gfx/geometry/rect_f.h b/ui/gfx/geometry/rect_f.h
index dc233a7..3b132667e 100644
--- a/ui/gfx/geometry/rect_f.h
+++ b/ui/gfx/geometry/rect_f.h
@@ -12,6 +12,10 @@
 #include "ui/gfx/geometry/size_f.h"
 #include "ui/gfx/geometry/vector2d_f.h"
 
+#if defined(OS_MACOSX)
+typedef struct CGRect CGRect;
+#endif
+
 namespace gfx {
 
 class InsetsF;
@@ -27,6 +31,12 @@ class GFX_EXPORT RectF {
   RectF(const PointF& origin, const SizeF& size)
       : origin_(origin), size_(size) {}
 
+#if defined(OS_MACOSX)
+  explicit RectF(const CGRect& r);
+  // Construct an equivalent CoreGraphics object.
+  CGRect ToCGRect() const;
+#endif
+
   ~RectF() {}
 
   float x() const { return origin_.x(); }