PageLoadMetrics: Remove unused callback OnFirstLayout

PageLoadMetricsObserverInterface::OnFirstLayout is not called from
anywhere. This CL removes the method.

Change-Id: I2bc9612c4c3f7890006868923b3a9a8e9c83894b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3779936
Reviewed-by: Kouhei Ueno <kouhei@chromium.org>
Reviewed-by: Takashi Toyoshima <toyoshim@chromium.org>
Commit-Queue: Ken Okada <kenoss@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1028580}

components/page_load_metrics/browser/page_load_metrics_forward_observer.cc

@@ -178,9 +178,6 @@ void PageLoadMetricsForwardObserver::OnDomContentLoadedEventStart(
 void PageLoadMetricsForwardObserver::OnLoadEventStart(
     const mojom::PageLoadTiming& timing) {}
 
-void PageLoadMetricsForwardObserver::OnFirstLayout(
-    const mojom::PageLoadTiming& timing) {}
-
 void PageLoadMetricsForwardObserver::OnParseStart(
     const mojom::PageLoadTiming& timing) {}
 

components/page_load_metrics/browser/page_load_metrics_forward_observer.h

@@ -81,7 +81,6 @@ class PageLoadMetricsForwardObserver final
   void OnDomContentLoadedEventStart(
       const mojom::PageLoadTiming& timing) override;
   void OnLoadEventStart(const mojom::PageLoadTiming& timing) override;
-  void OnFirstLayout(const mojom::PageLoadTiming& timing) override;
   void OnParseStart(const mojom::PageLoadTiming& timing) override;
   void OnParseStop(const mojom::PageLoadTiming& timing) override;
   void OnFirstPaintInPage(const mojom::PageLoadTiming& timing) override;

components/page_load_metrics/browser/page_load_metrics_observer.h

@@ -187,7 +187,6 @@ class PageLoadMetricsObserver : public PageLoadMetricsObserverInterface {
   void OnDomContentLoadedEventStart(
       const mojom::PageLoadTiming& timing) override {}
   void OnLoadEventStart(const mojom::PageLoadTiming& timing) override {}
-  void OnFirstLayout(const mojom::PageLoadTiming& timing) override {}
   void OnParseStart(const mojom::PageLoadTiming& timing) override {}
   void OnParseStop(const mojom::PageLoadTiming& timing) override {}
   void OnFirstPaintInPage(const mojom::PageLoadTiming& timing) override {}

components/page_load_metrics/browser/page_load_metrics_observer_interface.h

@@ -354,7 +354,6 @@ class PageLoadMetricsObserverInterface {
   virtual void OnDomContentLoadedEventStart(
       const mojom::PageLoadTiming& timing) = 0;
   virtual void OnLoadEventStart(const mojom::PageLoadTiming& timing) = 0;
-  virtual void OnFirstLayout(const mojom::PageLoadTiming& timing) = 0;
   virtual void OnParseStart(const mojom::PageLoadTiming& timing) = 0;
   virtual void OnParseStop(const mojom::PageLoadTiming& timing) = 0;