Coalesce damage rects that share an edge.

This fixes the Bloat HTTP page cycler regression, and allows me to remove the
hack I checked in to disable multiple-paints due to an observed DHTML page
cycler regression.

I added a new histogram, RW_IntermediatePaintRectCount, that would have shown
the problem clearly had it been there before.

I included some cleanup in PaintAggregator:
1- rename "r" to "existing_rect" for clarity
2- check for contained (i.e., redundant) invalidates up front

I also changed the opacity of the paint rects used when --show-paint-rects is
specified.  I find myself dogfooding with this command line option enabled, and
I want it to be a little less annoying but still just as useful.

R=brettw
BUG=29477
TEST=none

Review URL: http://codereview.chromium.org/464057

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@33949 0039d316-1c4b-4281-b951-d872f2087c98

3 files changed, 45 insertions, 0 deletions

diff --git a/base/gfx/rect.cc b/base/gfx/rect.cc
index 1e067e7..2a35575 100644
--- a/base/gfx/rect.cc
+++ b/base/gfx/rect.cc
@@ -225,6 +225,13 @@ Point Rect::CenterPoint() const {
   return Point(x() + (width() + 1) / 2, y() + (height() + 1) / 2);
 }
 
+bool Rect::SharesEdgeWith(const gfx::Rect& rect) const {
+  return (y() == rect.y() && height() == rect.height() &&
+             (x() == rect.right() || right() == rect.x())) ||
+         (x() == rect.x() && width() == rect.width() &&
+             (y() == rect.bottom() || bottom() == rect.y()));
+}
+
 }  // namespace gfx
 
 std::ostream& operator<<(std::ostream& out, const gfx::Rect& r) {
diff --git a/base/gfx/rect.h b/base/gfx/rect.h
index 2eef76c..c3c01ad 100644
--- a/base/gfx/rect.h
+++ b/base/gfx/rect.h
@@ -149,6 +149,10 @@ class Rect {
   // Returns the center of this rectangle.
   Point CenterPoint() const;
 
+  // Returns true if this rectangle shares an entire edge (i.e., same width or
+  // same height) with the given rectangle, and the rectangles do not overlap.
+  bool SharesEdgeWith(const gfx::Rect& rect) const;
+
  private:
   gfx::Point origin_;
   gfx::Size size_;
diff --git a/base/gfx/rect_unittest.cc b/base/gfx/rect_unittest.cc
index 50c789d..3562883 100644
--- a/base/gfx/rect_unittest.cc
+++ b/base/gfx/rect_unittest.cc
@@ -278,3 +278,37 @@ TEST(RectTest, IsEmpty) {
   EXPECT_FALSE(gfx::Rect(0, 0, 10, 10).IsEmpty());
   EXPECT_FALSE(gfx::Rect(0, 0, 10, 10).size().IsEmpty());
 }
+
+TEST(RectTest, SharesEdgeWith) {
+  gfx::Rect r(2, 3, 4, 5);
+
+  // Must be non-overlapping
+  EXPECT_FALSE(r.SharesEdgeWith(r));
+
+  gfx::Rect just_above(2, 1, 4, 2);
+  gfx::Rect just_below(2, 8, 4, 2);
+  gfx::Rect just_left(0, 3, 2, 5);
+  gfx::Rect just_right(6, 3, 2, 5);
+
+  EXPECT_TRUE(r.SharesEdgeWith(just_above));
+  EXPECT_TRUE(r.SharesEdgeWith(just_below));
+  EXPECT_TRUE(r.SharesEdgeWith(just_left));
+  EXPECT_TRUE(r.SharesEdgeWith(just_right));
+
+  // Wrong placement
+  gfx::Rect same_height_no_edge(0, 0, 1, 5);
+  gfx::Rect same_width_no_edge(0, 0, 4, 1);
+
+  EXPECT_FALSE(r.SharesEdgeWith(same_height_no_edge));
+  EXPECT_FALSE(r.SharesEdgeWith(same_width_no_edge));
+
+  gfx::Rect just_above_no_edge(2, 1, 5, 2);  // too wide
+  gfx::Rect just_below_no_edge(2, 8, 3, 2);  // too narrow
+  gfx::Rect just_left_no_edge(0, 3, 2, 6);   // too tall
+  gfx::Rect just_right_no_edge(6, 3, 2, 4);  // too short
+
+  EXPECT_FALSE(r.SharesEdgeWith(just_above_no_edge));
+  EXPECT_FALSE(r.SharesEdgeWith(just_below_no_edge));
+  EXPECT_FALSE(r.SharesEdgeWith(just_left_no_edge));
+  EXPECT_FALSE(r.SharesEdgeWith(just_right_no_edge));
+}