Use static_cast instead of reinterpret_cast for downcasting

static_cast is better suited for downcasting since it can check that the
types are related.

/content/browser/renderer_host
This CL was uploaded by git cl split.

R=sadrul@chromium.org

Change-Id: I69d9a771d2470aeab73853b6f2468a9c5c507645
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2435882
Auto-Submit: Kevin McNee <mcnee@chromium.org>
Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Commit-Queue: Sadrul Chowdhury <sadrul@chromium.org>
Cr-Commit-Position: refs/heads/master@{#811357}

content/browser/renderer_host/render_process_host_browsertest.cc

@@ -280,8 +280,8 @@ IN_PROC_BROWSER_TEST_F(RenderProcessHostTest,
   RenderProcessHost* rph =
       shell()->web_contents()->GetMainFrame()->GetProcess();
   // Make it believe it's a guest.
-  reinterpret_cast<RenderProcessHostImpl*>(rph)->
-      set_is_for_guests_only_for_testing(true);
+  static_cast<RenderProcessHostImpl*>(rph)->set_is_for_guests_only_for_testing(
+      true);
   EXPECT_EQ(1, RenderProcessHost::GetCurrentRenderProcessCountForTesting());
 
   // Navigate to a different page.