Ensure RenderViewHost is not shut down until a screenshot of the page is taken.

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 1e066323ea29f8bc3489be9fb0b9554d73b36987..473dbe15a5c39c191df426ba6140475f8855aa0d 100644
--- a/content/browser/frame_host/navigation_entry_screenshot_manager.cc
+++ b/content/browser/frame_host/navigation_entry_screenshot_manager.cc
@@ -150,9 +150,10 @@ void NavigationEntryScreenshotManager::SetMinScreenshotIntervalMS(
   min_screenshot_interval_ms_ = interval_ms;
 }
 
-void NavigationEntryScreenshotManager::OnScreenshotTaken(int unique_id,
-                                                     bool success,
-                                                     const SkBitmap& bitmap) {
+void NavigationEntryScreenshotManager::OnScreenshotTaken(
+    int unique_id,
+    bool success,
+    const SkBitmap& bitmap) {
   NavigationEntryImpl* entry = NULL;
   int entry_count = owner_->GetEntryCount();
   for (int i = 0; i < entry_count; ++i) {
@@ -169,8 +170,7 @@ void NavigationEntryScreenshotManager::OnScreenshotTaken(int unique_id,
   }
 
   if (!success || bitmap.empty() || bitmap.isNull()) {
-    if (!ClearScreenshot(entry))
-      OnScreenshotSet(entry);
+    ClearScreenshot(entry);
     return;
   }
 
@@ -215,8 +215,8 @@ void NavigationEntryScreenshotManager::OnScreenshotEncodeComplete(
 
 void NavigationEntryScreenshotManager::OnScreenshotSet(
     NavigationEntryImpl* entry) {
-  if (entry->screenshot().get())
-    PurgeScreenshotsIfNecessary();
+  CHECK(entry->screenshot().get());
+  PurgeScreenshotsIfNecessary();
 }
 
 bool NavigationEntryScreenshotManager::ClearScreenshot(