Stop tracking user input events without a relevant load.

These events are 100x more common than other errors. User input events
can arrive when the user is e.g. looking at an image, which isn't a
tracked page but is something a user can interact with, so it's valid
to receive input events without a committed load. Thus, it doesn't make
sense to log this error.

Review-Url: https://codereview.chromium.org/2142743002
Cr-Commit-Position: refs/heads/master@{#405286}

components/page_load_metrics/browser/metrics_web_contents_observer.cc

@@ -786,12 +786,8 @@ void MetricsWebContentsObserver::OnInputEvent(
   if (event.type == blink::WebInputEvent::Type::Undefined)
     return;
 
-  if (!committed_load_) {
-    RecordInternalError(ERR_USER_INPUT_WITH_NO_RELEVANT_LOAD);
-    return;
-  }
-
-  committed_load_->OnInputEvent(event);
+  if (committed_load_)
+    committed_load_->OnInputEvent(event);
 }
 
 void MetricsWebContentsObserver::DidRedirectNavigation(

components/page_load_metrics/browser/metrics_web_contents_observer.h

@@ -89,8 +89,11 @@ enum InternalErrorLoadEvent {
   // latest aborted load is used to track the chain size.
   ERR_NAVIGATION_SIGNALS_MULIPLE_ABORTED_LOADS,
 
-  // Receives user input before navigation start
-  ERR_USER_INPUT_WITH_NO_RELEVANT_LOAD,
+  // Received user input without a relevant load. This error type is deprecated,
+  // as it is valid to receive user input without a relevant load. We leave the
+  // enum value here since it's also used in histogram recording, so it's
+  // important that we not re-use this enum entry for a different value.
+  DEPRECATED_ERR_USER_INPUT_WITH_NO_RELEVANT_LOAD,
 
   // A TimeTicks value in the browser process has value less than
   // navigation_start_. This could happen if navigation_start_ was computed in