cc/blimp: Add (de)-serialization for PictureLayer and ScrollbarLayer.

cc/proto/layer.proto

Index: cc/proto/layer.proto
diff --git a/cc/proto/layer.proto b/cc/proto/layer.proto
index b4b6035575bbdb470851985c456787d75e5fcd53..2d211baceaed0391e1ef2f14f0e3ba21244ec4f8 100644
--- a/cc/proto/layer.proto
+++ b/cc/proto/layer.proto
@@ -44,6 +44,9 @@ message LayerNode {
   // A List of all the children of the current LayerNode.
   repeated LayerNode children = 4;
   optional LayerNode mask_layer = 5;
+
+  // Set for SolidColorScrollbarLayers.
+  optional SolidColorScrollbarLayerProperties solid_scrollbar = 7;
 }
 
 // A container for a list of dirty layers.
@@ -65,7 +68,6 @@ message LayerProperties {
   // TODO(dtrainor): use a 'oneof' union when it's supported in Chromium.  See
   // crbug.com/570371.
   optional PictureLayerProperties picture = 6;
-  optional SolidColorScrollbarLayerProperties solid_scrollbar = 7;
 }
 
 // NEXT ID: 59
@@ -146,16 +148,19 @@ message BaseLayerProperties {
 }
 
 message PictureLayerProperties {
+  // The following fields mirror the data stored in
+  // PictureLayer::PictureLayerInputs.------------------------

[vmpstr, 2016/10/07 23:50:05]

Style nit: do you really need -----, can we just separate blocks as

// This is blah.
one
two
three

four
five
six

is it clear that one two and three are blah but four five and six aren't?

[Khushal, 2016/10/08 00:41:33]

I did it in the layer proto so did it here just to be consistent. Wouldn't worry
about this too much, its going to go away soon anyway.

+  optional bool nearest_neighbor = 5;
+  optional Rect recorded_viewport = 7;
+  optional DisplayItemList display_list = 8;
+  // --------------------------------------------------------
+
+  // TODO(khushalsagar): Remove these when crbug.com/648442
   optional RecordingSource recording_source = 1;
   optional Region invalidation = 2;
   optional Rect last_updated_visible_layer_rect = 3;
   optional bool is_mask = 4;
-  optional bool nearest_neighbor = 5;
-
   optional int64 update_source_frame_number = 6;
-
-  optional Rect recorded_viewport = 7;
-  optional DisplayItemList display_list = 8;
 }
 
 message SolidColorScrollbarLayerProperties {