[wip] Add some more state to RenderViewHost's lifetime.

content/browser/frame_host/navigation_entry_screenshot_manager.cc

Index: content/browser/frame_host/navigation_entry_screenshot_manager.cc
diff --git a/content/browser/frame_host/navigation_entry_screenshot_manager.cc b/content/browser/frame_host/navigation_entry_screenshot_manager.cc
index b2bf429dc0a6c66a34266a5267ed62267a8aacb6..85bd93595ce81b66c1fca19ce28ed4eed90efc70 100644
--- a/content/browser/frame_host/navigation_entry_screenshot_manager.cc
+++ b/content/browser/frame_host/navigation_entry_screenshot_manager.cc
@@ -166,8 +166,7 @@ void NavigationEntryScreenshotManager::OnScreenshotTaken(int unique_id,
   }
 
   if (!success || bitmap.empty() || bitmap.isNull()) {
-    if (!ClearScreenshot(entry))
-      OnScreenshotSet(entry);
+    ClearScreenshot(entry);
     return;
   }
 
@@ -212,8 +211,8 @@ void NavigationEntryScreenshotManager::OnScreenshotEncodeComplete(
 
 void NavigationEntryScreenshotManager::OnScreenshotSet(
     NavigationEntryImpl* entry) {
-  if (entry->screenshot().get())
-    PurgeScreenshotsIfNecessary();
+  CHECK(entry->screenshot().get());
+  PurgeScreenshotsIfNecessary();
 }
 
 bool NavigationEntryScreenshotManager::ClearScreenshot(