Revert "cc: Move canvas clear from picture to picture_pile_impl"

cc/resources/picture_pile_impl.cc

Index: cc/resources/picture_pile_impl.cc
diff --git a/cc/resources/picture_pile_impl.cc b/cc/resources/picture_pile_impl.cc
index 865e878ac75a1d1894775a3435937c69bd6164ff..6299e29988dda5597898050af5ddc9d44afa2ad2 100644
--- a/cc/resources/picture_pile_impl.cc
+++ b/cc/resources/picture_pile_impl.cc
@@ -96,25 +96,15 @@ void PicturePileImpl::Raster(
   gfx::Rect content_rect = total_content_rect;
   content_rect.Intersect(canvas_rect);
 
-  // Clear one texel inside the right/bottom edge of the content rect,
-  // as it may only be partially covered by the picture playback.
-  // Also clear one texel outside the right/bottom edge of the content rect,
-  // as it may get blended in by linear filtering when zoomed in.
-  gfx::Rect deflated_content_rect = total_content_rect;
-  deflated_content_rect.Inset(0, 0, 1, 1);
-
-  gfx::Rect canvas_outside_content_rect = canvas_rect;
-  canvas_outside_content_rect.Subtract(deflated_content_rect);
-
-  if (!canvas_outside_content_rect.IsEmpty()) {
-    gfx::Rect inflated_content_rect = total_content_rect;
-    inflated_content_rect.Inset(0, 0, -1, -1);
-    canvas->clipRect(gfx::RectToSkRect(inflated_content_rect),
-                     SkRegion::kReplace_Op);
-    canvas->clipRect(gfx::RectToSkRect(deflated_content_rect),
-                     SkRegion::kDifference_Op);
-    canvas->drawColor(background_color_, SkXfermode::kSrc_Mode);
-  }
+  // Clear an inflated content rect, to ensure that we always sample
+  // a correct pixel.
+  gfx::Rect inflated_content_rect = total_content_rect;
+  inflated_content_rect.Inset(0, 0, -1, -1);
+
+  SkPaint background_paint;
+  background_paint.setColor(background_color_);
+  background_paint.setXfermodeMode(SkXfermode::kSrc_Mode);
+  canvas->drawRect(RectToSkRect(inflated_content_rect), background_paint);

[Tom Hudson, 2013/04/30 09:43:59]

canvas->clear(background_color_) may be more efficient, or equally efficient and
more legible?

(2 forms of efficiency: (1) it used to be strictly more performant; we've tried
to fix that; (2) it keeps the picture simpler, with fewer unique paints.)

[vmpstr, 2013/04/30 17:06:23]

Fixed.

[enne (OOO), 2013/04/30 17:13:53]

Sometimes we are only rastering a sub-rectangle of a texture.  If you do an
unclipped clear here, this will likely end up rastering unneeded pixels.  (For
hardware the clear's faster, but maybe not for software?)  If you're going to
change drawRect to a clear, should it not move after the clipRect?

 
   // Rasterize the collection of relevant picture piles.
   gfx::Rect layer_rect = gfx::ToEnclosingRect(