Change cc::ElementId to be a uint64_t

third_party/WebKit/Source/core/offscreencanvas/OffscreenCanvas.h

Index: third_party/WebKit/Source/core/offscreencanvas/OffscreenCanvas.h
diff --git a/third_party/WebKit/Source/core/offscreencanvas/OffscreenCanvas.h b/third_party/WebKit/Source/core/offscreencanvas/OffscreenCanvas.h
index 3d5b7820d210832b2a1f854bdb9c52183ed40784..eefa999aaec147411c1b78d56b9cd1b592e8d7ab 100644
--- a/third_party/WebKit/Source/core/offscreencanvas/OffscreenCanvas.h
+++ b/third_party/WebKit/Source/core/offscreencanvas/OffscreenCanvas.h
@@ -59,10 +59,10 @@ class CORE_EXPORT OffscreenCanvas final
   const IntSize& Size() const override { return size_; }
   void SetSize(const IntSize&);
 
-  void SetPlaceholderCanvasId(int canvas_id) {
+  void SetPlaceholderCanvasId(unsigned canvas_id) {

[suzyh_UTC10 (ex-contributor), 2017/05/05 04:27:30]

Would it be worth typedef-ing canvas ID as well, to aid in having
self-documenting code?

[chrishtr, 2017/05/05 05:34:52]

Sure - done.

     placeholder_canvas_id_ = canvas_id;
   }
-  int PlaceholderCanvasId() const { return placeholder_canvas_id_; }
+  unsigned PlaceholderCanvasId() const { return placeholder_canvas_id_; }
   bool HasPlaceholderCanvas() {
     return placeholder_canvas_id_ != kNoPlaceholderCanvas;
   }
@@ -167,10 +167,10 @@ class CORE_EXPORT OffscreenCanvas final
   WeakMember<ExecutionContext> execution_context_;
 
   enum {
-    kNoPlaceholderCanvas = -1,  // DOMNodeIds starts from 0, using -1 to
-                                // indicate no associated canvas element.
+    kNoPlaceholderCanvas = 0,  // DOMNodeIds starts from 1, using 0 to

[chrishtr, 2017/05/05 03:40:11]

https://cs.chromium.org/chromium/src/third_party/WebKit/Source/core/dom/WeakI...

always returns a value > 0.

[suzyh_UTC10 (ex-contributor), 2017/05/05 04:27:30]

What is the practical result of changing this from -1 to 0? Are there any tests
that need to be changed (or added) to ensure that this change has not got out of
sync with the assumptions baked into any other part of the code?

[chrishtr, 2017/05/05 05:34:52]

I made this change because bit-shifting signed integers is weird.
I think the practical change should be nothing, because
kNoPlaceholderCanvas was just the initialized value of
placeholder_canvas_id_ before being set. So either way the
code is able to detect whether the placeholder_canvas_id was set.
Re tests changed: I guess not, since they seem to pass.
Re added: I think existing tests should exercise the code,
as well as the DCHECK in DomNodeIds. I'll wait for feedback from
junov@ on this also.

+                               // indicate no associated canvas element.
   };
-  int placeholder_canvas_id_ = kNoPlaceholderCanvas;
+  unsigned placeholder_canvas_id_ = kNoPlaceholderCanvas;
 
   IntSize size_;
   bool is_neutered_ = false;