Fix cc scrollbar layer issues with initialization, and use element ids throughout.

third_party/WebKit/Source/platform/graphics/CompositorElementId.h

Index: third_party/WebKit/Source/platform/graphics/CompositorElementId.h
diff --git a/third_party/WebKit/Source/platform/graphics/CompositorElementId.h b/third_party/WebKit/Source/platform/graphics/CompositorElementId.h
index df3954953bf83844c7cc5b04bddbb4f5a60de2a8..1c1e858a4a6bbf6d20d14da3c0f89ef8f1e050c6 100644
--- a/third_party/WebKit/Source/platform/graphics/CompositorElementId.h
+++ b/third_party/WebKit/Source/platform/graphics/CompositorElementId.h
@@ -13,20 +13,20 @@
 
 namespace blink {
 
-enum class CompositorSubElementId {
+enum class CompositorElementIdNamespace {
   kPrimary,
   kScroll,
   kViewport,
   kLinkHighlight,
+  kScrollbar,
   // A sentinel to indicate how many enum values there are.
-  kNumSubElementTypes
+  kMaxRepresentableNamespaceId = 8

[wkorman, 2017/05/12 22:29:39]

Could define kNamespaceBits = 3 above/somewhere, and then use = 1 <<
kNamespaceBits here, and also use it in the .cpp file.

[chrishtr, 2017/05/12 23:44:16]

Great idea! Done. Xianzhu++, it was his idea from elsewhere.

 };
 
 using CompositorElementId = cc::ElementId;
-using DOMNodeId = uint64_t;
 
 CompositorElementId PLATFORM_EXPORT
-    CreateCompositorElementId(DOMNodeId, CompositorSubElementId);
+CreateCompositorElementId(uint64_t id, CompositorElementIdNamespace);

[wkorman, 2017/05/12 22:29:39]

Is conflict between scrollbar id and dom node id not possible due to additional
use of namespace? Are we ok with that as the only safeguard.

[chrishtr, 2017/05/12 23:44:16]

Done.

 
 // Note cc::ElementId has a hash function already implemented via
 // ElementIdHash::operator(). However for consistency's sake we choose to use
@@ -42,9 +42,9 @@ struct CompositorElementIdHash {
   static const bool safe_to_compare_to_empty_or_deleted = true;
 };
 
-DOMNodeId PLATFORM_EXPORT DomNodeIdFromCompositorElementId(CompositorElementId);
-CompositorSubElementId PLATFORM_EXPORT
-    SubElementIdFromCompositorElementId(CompositorElementId);
+uint64_t PLATFORM_EXPORT IdFromCompositorElementId(CompositorElementId);
+CompositorElementIdNamespace PLATFORM_EXPORT
+    NamespaceFromCompositorElementId(CompositorElementId);
 
 struct CompositorElementIdHashTraits
     : WTF::GenericHashTraits<CompositorElementId> {