Expose IsSolidColor and write units tests

cc/resources/picture_pile.cc

Index: cc/resources/picture_pile.cc
diff --git a/cc/resources/picture_pile.cc b/cc/resources/picture_pile.cc
index 128b1491714dcd1d33c2585bd0d4d726389a6195..254d2b7ee6301bec20957487a87c9bd16117634c 100644
--- a/cc/resources/picture_pile.cc
+++ b/cc/resources/picture_pile.cc
@@ -19,6 +19,9 @@ namespace {
 // picture that intersects the visible layer rect expanded by this distance
 // will be recorded.
 const int kPixelDistanceToRecord = 8000;
+// We don't perform solid color analysis on images that have more than 10 skia
+// operations.
+const int kOpCountThatIsOkToAnalyze = 10;
 
 // TODO(humper): The density threshold here is somewhat arbitrary; need a
 // way to set // this from the command line so we can write a benchmark
@@ -146,7 +149,11 @@ float ClusterTiles(const std::vector<gfx::Rect>& invalid_tiles,
 
 namespace cc {
 
-PicturePile::PicturePile() : is_suitable_for_gpu_rasterization_(true) {}
+PicturePile::PicturePile()
+    : is_suitable_for_gpu_rasterization_(true),
+      is_solid_color_(true),
+      solid_color_(SK_ColorTRANSPARENT) {
+}
 
 PicturePile::~PicturePile() {
 }
@@ -501,6 +508,7 @@ bool PicturePile::UpdateAndExpandInvalidation(
         found_tile_for_recorded_picture = true;
       }
     }
+    DetermineIfSolidColor();
     DCHECK(found_tile_for_recorded_picture);
   }
 
@@ -516,4 +524,37 @@ void PicturePile::SetEmptyBounds() {
   recorded_viewport_ = gfx::Rect();
 }
 
+void PicturePile::DetermineIfSolidColor() {
+  is_solid_color_ = false;
+  solid_color_ = SK_ColorTRANSPARENT;
+
+  // Determine if the entire picture map is pointing to the same image.
+  if (picture_map_.empty()) {
+    is_solid_color_ = true;  // No pictures? Then we're solid 100% transparent.

[enne (OOO), 2014/08/25 23:21:07]

Is this true? I think the map being empty is maybe only possible if the bounds
are empty.

[hendrikw, 2014/08/26 00:12:38]

I don't think we should ever rasterize a picture_pile with an empty map, so it
doesn't really matter what we set it to.  I tried a
DCHECK(!picture_map_.empty()) in PicturePileImpl::RasterForAnalysis and went to
a bunch of sites, never hit.

I've changed the comment, my preference is to still set it to true, but I'm fine
with false too.

I could add the DCHECK to the final code to backup my assumption.

+    return;
+  }
+
+  PictureMap::const_iterator it = picture_map_.begin();
+  const Picture* picture = it->second.GetPicture();
+
+  // There are situations where the first picture is NULL, we'll assume not

[enne (OOO), 2014/08/25 23:21:07]

"There are situations where the first picture is NULL" => "Missing recordings
due to frequent invalidations or being too far away from the interest rect"

[hendrikw, 2014/08/26 00:12:37]

Done.

+  // solid in this case.
+  if (!picture)
+    return;
+
+  // Don't bother doing more work if the first image is too complicated.
+  if (picture->ApproximateOpCount() > kOpCountThatIsOkToAnalyze)
+    return;
+
+  // Make sure all of the mapped images point to the same picture.
+  for (++it; it != picture_map_.end(); ++it) {
+    if (it->second.GetPicture() != picture)
+      return;
+  }
+  skia::AnalysisCanvas canvas(recorded_viewport_.width(),
+                              recorded_viewport_.height());
+  picture->Raster(&canvas, NULL, Region(), 1.0f);
+  is_solid_color_ = canvas.GetColorIfSolid(&solid_color_);
+}
+
 }  // namespace cc