[DNR] Add documentation for getMatchedRules quota under user gestures

This CL adds documentation which states that the quota for
getMatchedRules calls does not apply if the call is associated with a
user gesture.

Bug: 1044702
Change-Id: I2a2ed5deacc674ba86aef744094b3c1935c4ab91
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2085591
Commit-Queue: Kelvin Jiang <kelvinjiang@chromium.org>
Commit-Queue: Karan Bhatia <karandeepb@chromium.org>
Auto-Submit: Kelvin Jiang <kelvinjiang@chromium.org>
Reviewed-by: Karan Bhatia <karandeepb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#746524}

extensions/common/api/declarative_net_request.idl

@@ -381,6 +381,8 @@ namespace declarativeNetRequest {
     // Time interval within which <code>MAX_GETMATCHEDRULES_CALLS_PER_INTERVAL
     // getMatchedRules</code> calls can be made, specified in minutes.
     // Additional calls will fail immediately and set $(ref:runtime.lastError).
+    // Note: <code>getMatchedRules</code> calls associated with a user gesture
+    // are exempt from the quota.
     [value=10] static long GETMATCHEDRULES_QUOTA_INTERVAL();
 
     // The number of times <code>getMatchedRules</code> can be called within a