Update PageHint comments to match optimizationguide.proto

Change-Id: I12818936e2ebd71c43e7ad42df4a3167f8a107b3
Reviewed-on: https://chromium-review.googlesource.com/c/1316249Reviewed-by: Tarun Bansal <tbansal@chromium.org>
Commit-Queue: Jered Gray <jegray@chromium.org>
Cr-Commit-Position: refs/heads/master@{#605074}

components/optimization_guide/proto/hints.proto

@@ -120,9 +120,10 @@ message PageHint {
   // The maximum effective connection type threshold for triggering the
   // optimization associated with this hint.
   optional EffectiveConnectionType max_ect_trigger = 2;
-  // An ordered list of optimizations that should be whitelisted for this page
-  // pattern. The client uses the first optimization in this list that is
-  // enabled for it.
+  // An ordered set of optimizations that should be whitelisted for this page
+  // pattern.
+  //
+  // The client will use the first optimization that it supports.
   repeated Optimization whitelisted_optimizations = 3;
 }