Add powerEfficient[En/De]coder (#666) and fingerprint mitigations (#675…

…). (#670)

* Fixes #666

* Add fingerprint warning

* Fix #675

* Add 'check if hardware exposure is allowed' algorithm

* Remove double-the

webrtc-stats.html

@@ -356,6 +356,39 @@ <h3>
         </p>
       </section>
     </section>
+    <section>
+      <h2>
+        Privacy considerations
+      </h2>
+      <p class="fingerprint">
+        The WebRTC's Statistics API exposes information about the system,
+        including hardware capabilities and network characteristics. To limit
+        the finger printing surface imposed by this API, some metrics are only
+        exposed if allowed by the algorithms in this section.
+      </p>
+      <section>
+        <h3>
+          Limiting exposure of hardware capabilities
+        </h3>
+        <p>
+          To <dfn data-lt="exposing hardware is allowed">check if hardware
+          exposure is allowed</dfn>, run the following steps:
+          <ol>
+            <li>
+              <p>
+                If the <a href="https://w3c.github.io/mediacapture-main/#context-capturing-state">
+                context capturing state</a> is true, return true.
+              </p>
+            </li>
+            <li>
+              <p>
+                Return false.
+              </p>
+            </li>
+          </ol>
+        </p>
+      </section>
+    </section>
     <section id="rtctatstype-*">
       <h2>
         {{RTCStatsType}}
@@ -961,6 +994,7 @@ <h3>
              unsigned long        framesReceived;
              DOMString            decoderImplementation;
              DOMString            playoutId;
+             boolean              powerEfficientDecoder;
             };</pre>
           <section>
             <h2>
@@ -1509,13 +1543,12 @@ <h2>
                 "idlMemberType">DOMString</span>
               </dt>
               <dd>
-                <p>
-                  Identifies the decoder implementation used. This is useful for diagnosing
-                  interoperability issues.
-                </p>
                 <p class="fingerprint">
-                  If too much information is given here, it increases the fingerprint surface.
-                  Since it is only given for active tracks, the incremental exposure is small.
+                  Only defined when [= exposing hardware is allowed =].
+                </p>
+                <p>
+                  Identifies the decoder implementation used. This is useful for
+                  diagnosing interoperability issues.
                 </p>
               </dd>
               <dt>
@@ -1528,6 +1561,22 @@ <h2>
                   corresponding {{RTCAudioPlayoutStats}}.
                 </p>
               </dd>
+              <dt>
+                <dfn>powerEfficientDecoder</dfn> of type <span class=
+                "idlMemberType">boolean</span>
+              </dt>
+              <dd>
+                <p class="fingerprint">
+                  Only defined when [= exposing hardware is allowed =].
+                </p>
+                <p>
+                  Whether the decoder currently used is considered power
+                  efficient by the user agent. This SHOULD reflect if the
+                  configuration results in hardware acceleration, but the user
+                  agent MAY take other information into account when deciding if
+                  the configuration is considered power efficient.
+                </p>
+              </dd>
             </dl>
           </section>
         </div>
@@ -1692,6 +1741,7 @@ <h3>
              unsigned long        firCount;
              unsigned long        pliCount;
              DOMString            encoderImplementation;
+             boolean              powerEfficientEncoder;
              boolean              active;
 };</pre>
           <section>
@@ -2030,13 +2080,28 @@ <h2>
                 "idlMemberType">DOMString</span>
               </dt>
               <dd>
+                <p class="fingerprint">
+                  Only defined when [= exposing hardware is allowed =].
+                </p>
                 <p>
                   Identifies the encoder implementation used. This is useful for diagnosing
                   interoperability issues.
                 </p>
+              </dd>
+              <dt>
+                <dfn>powerEfficientEncoder</dfn> of type <span class=
+                "idlMemberType">boolean</span>
+              </dt>
+              <dd>
                 <p class="fingerprint">
-                  If too much information is given here, it increases the fingerprint surface.
-                  Since it is only given for active tracks, the incremental exposure is small.
+                  Only defined when [= exposing hardware is allowed =].
+                </p>
+                <p>
+                  Whether the encoder currently used is considered power
+                  efficient by the user agent. This SHOULD reflect if the
+                  configuration results in hardware acceleration, but the user
+                  agent MAY take other information into account when deciding if
+                  the configuration is considered power efficient.
                 </p>
               </dd>
               <dt>