cc: Do not create separate tilings for almost equal scale factors.

cc/layers/picture_layer_impl.cc

Index: cc/layers/picture_layer_impl.cc
diff --git a/cc/layers/picture_layer_impl.cc b/cc/layers/picture_layer_impl.cc
index f8aa213a92596eef4bcf8a843933d4c1d6f10da2..f7da43ec84514b2aefd34bacc1b92d82ac96724f 100644
--- a/cc/layers/picture_layer_impl.cc
+++ b/cc/layers/picture_layer_impl.cc
@@ -48,6 +48,12 @@ const int kMinHeightForGpuRasteredTile = 256;
 // of using the same tile size.
 const int kTileRoundUp = 64;
 
+// The precision value for rounding floating points values of scale factors.
+// With this scale factors will be having 3 digits fractional part, which will
+// make almost equal (having smaller difference by some magnitude of floating
+// point epsilon) scale factors to be considered as same.
+const int kScalePrecision = 4;
+
 }  // namespace
 
 namespace cc {
@@ -1187,11 +1193,14 @@ void PictureLayerImpl::UpdateIdealScales() {
   float min_contents_scale = MinimumContentsScale();
   DCHECK_GT(min_contents_scale, 0.f);
 
-  ideal_page_scale_ = IsAffectedByPageScale()
-                          ? layer_tree_impl()->current_page_scale_factor()
-                          : 1.f;
+  ideal_page_scale_ =
+      IsAffectedByPageScale()
+          ? MathUtil::RoundToFixedPrecision(
+                layer_tree_impl()->current_page_scale_factor(), kScalePrecision)
+          : 1.f;
   ideal_device_scale_ = layer_tree_impl()->device_scale_factor();
-  ideal_contents_scale_ = std::max(GetIdealContentsScale(), min_contents_scale);
+  ideal_contents_scale_ = MathUtil::RoundToFixedPrecision(
+      std::max(GetIdealContentsScale(), min_contents_scale), kScalePrecision);

[prashant.n, 2015/10/26 16:35:04]

Modifying ideal page and contents scales are needed as they are checked against
in ShouldAdjustRasterScale() and RecalculateRasterScales() functions.

   ideal_source_scale_ =
       ideal_contents_scale_ / ideal_page_scale_ / ideal_device_scale_;
 }