cc: Remove CHECKs for valid property tree indices

These were added to help catch bugs and understand crashes while
property trees were being implemented.

Converting them to DCHECKs improves draw property computation time
(as measured locally on Linux using CalcDrawPropsTest cc perftests)
by about 14%.

BUG=489856
CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_trusty_blink_rel

Review-Url: https://codereview.chromium.org/2644603002
Cr-Commit-Position: refs/heads/master@{#444425}

cc/trees/property_tree.h

@@ -65,13 +65,11 @@ class CC_EXPORT PropertyTree {
   int Insert(const T& tree_node, int parent_id);
 
   T* Node(int i) {
-    // TODO(vollick): remove this.
-    CHECK(i < static_cast<int>(nodes_.size()));
+    DCHECK(i < static_cast<int>(nodes_.size()));
     return i > kInvalidNodeId ? &nodes_[i] : nullptr;
   }
   const T* Node(int i) const {
-    // TODO(vollick): remove this.
-    CHECK(i < static_cast<int>(nodes_.size()));
+    DCHECK(i < static_cast<int>(nodes_.size()));
     return i > kInvalidNodeId ? &nodes_[i] : nullptr;
   }