[content] Do not unnecessarily handle delegated_frame_host_ being null in RenderWidgetHostViewMac.

This is a cleanup prior to fixing crbug.com/1164477. It improves
readability by removing code that handles situations that never occur.

Bug: 1164477
Change-Id: Ia9356857eb82e75d8d3527e278036c12dfdc636d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2618183
Commit-Queue: Charlie Reis <creis@chromium.org>
Auto-Submit: François Doray <fdoray@chromium.org>
Reviewed-by: Charlie Reis <creis@chromium.org>
Reviewed-by: danakj <danakj@chromium.org>
Cr-Commit-Position: refs/heads/master@{#843683}

content/browser/renderer_host/render_widget_host_view_mac.mm

@@ -445,9 +445,6 @@ void RenderWidgetHostViewMac::WasUnOccluded() {
 
   browser_compositor_->SetRenderWidgetHostIsHidden(false);
 
-  DelegatedFrameHost* delegated_frame_host =
-      browser_compositor_->GetDelegatedFrameHost();
-
   bool has_saved_frame =
       browser_compositor_->has_saved_frame_before_state_transition();
 
@@ -458,17 +455,18 @@ void RenderWidgetHostViewMac::WasUnOccluded() {
                        ? tab_switch_start_state.Clone()
                        : blink::mojom::RecordContentToVisibleTimeRequestPtr());
 
-  if (delegated_frame_host) {
-    // If the frame for the renderer is already available, then the
-    // tab-switching time is the presentation time for the browser-compositor.
-    const bool record_presentation_time = has_saved_frame;
-    delegated_frame_host->WasShown(
-        browser_compositor_->GetRendererLocalSurfaceId(),
-        browser_compositor_->GetRendererSize(),
-        record_presentation_time
-            ? std::move(tab_switch_start_state)
-            : blink::mojom::RecordContentToVisibleTimeRequestPtr());
-  }
+  // If the frame for the renderer is already available, then the
+  // tab-switching time is the presentation time for the browser-compositor.
+  DelegatedFrameHost* delegated_frame_host =
+      browser_compositor_->GetDelegatedFrameHost();
+  DCHECK(delegated_frame_host);
+  const bool record_presentation_time = has_saved_frame;
+  delegated_frame_host->WasShown(
+      browser_compositor_->GetRendererLocalSurfaceId(),
+      browser_compositor_->GetRendererSize(),
+      record_presentation_time
+          ? std::move(tab_switch_start_state)
+          : blink::mojom::RecordContentToVisibleTimeRequestPtr());
 }
 
 void RenderWidgetHostViewMac::WasOccluded() {