Avoid exposing cc::Layer tree to CompositorProxy

third_party/WebKit/Source/core/dom/CompositorProxy.cpp

Index: third_party/WebKit/Source/core/dom/CompositorProxy.cpp
diff --git a/third_party/WebKit/Source/core/dom/CompositorProxy.cpp b/third_party/WebKit/Source/core/dom/CompositorProxy.cpp
index ad9ccd3379ce1cf62e31996cc32efe450b32e54b..0b0026b1cbe698c65a8f10d15ebec46464fc4bdb 100644
--- a/third_party/WebKit/Source/core/dom/CompositorProxy.cpp
+++ b/third_party/WebKit/Source/core/dom/CompositorProxy.cpp
@@ -19,6 +19,11 @@
 #include <algorithm>
 
 namespace blink {
+namespace {
+// An identifier for CompositorProxy objects. Will be unique across all proxies
+// created in the same thread.
+uint64_t g_unique_id = 0;
+}  // namespace
 
 static const struct {
   const char* name;
@@ -137,7 +142,8 @@ CompositorProxy* CompositorProxy::Create(
 
 CompositorProxy::CompositorProxy(uint64_t element_id,
                                  uint32_t compositor_mutable_properties)
-    : element_id_(element_id),
+    : proxy_id_(g_unique_id++),
+      element_id_(element_id),
       compositor_mutable_properties_(compositor_mutable_properties),
       client_(nullptr) {
   DCHECK(compositor_mutable_properties_);