NavigationController: Fix several broken class invariants.

content/public/browser/navigation_controller.h

Index: content/public/browser/navigation_controller.h
diff --git a/content/public/browser/navigation_controller.h b/content/public/browser/navigation_controller.h
index 4ece52b3df2a8e9ec780379c87938f386fa81ccf..0ba67b66a3f86d43073326d6ea19c9a7e457e0b1 100644
--- a/content/public/browser/navigation_controller.h
+++ b/content/public/browser/navigation_controller.h
@@ -268,7 +268,8 @@ class NavigationController {
   // committed entries.
   virtual NavigationEntry* GetLastCommittedEntry() const = 0;
 
-  // Returns the index of the last committed entry.
+  // Returns the index of the last committed entry.  It will be -1 iff there are
+  // no entries.

[Charlie Reis, 2017/04/24 17:34:55]

As you pointed out, this isn't true.  Let's rephrase:

It will be -1 if there are no entries, or if there is a transient entry before
the first entry commits.

[arthursonzogni, 2017/04/26 12:13:48]

Done.

   virtual int GetLastCommittedEntryIndex() const = 0;
 
   // Returns true if the source for the current entry can be viewed.