Omnibox Metrics: Make |completed_length| field sane

Have no qualms about fixing the definition of this broken field.  (No
need to deprecate the field and create a new one.)

See bug link for details.

The internal proto change has been submitted.

TBR=pkasting

BUG=381650

Review URL: https://codereview.chromium.org/314113009

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@275651 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/omnibox/omnibox_log.h

@@ -73,8 +73,10 @@ struct OmniboxLog {
   base::TimeDelta elapsed_time_since_user_first_modified_omnibox;
 
   // The number of extra characters the user would have to manually type
-  // if she/he were not given the opportunity to select this match.  Set to
-  // base::string16::npos if not available.
+  // if she/he were not given the opportunity to select this match.  Only
+  // set for matches that are allowed to be the default match (i.e., are
+  // inlineable).  Set to base::string16::npos if the match is not allowed
+  // to be the default match.
   size_t completed_length;
 
   // The amount of time since the last time the default (i.e., inline)

chrome/browser/ui/omnibox/omnibox_edit_model.cc

@@ -756,7 +756,8 @@ void OmniboxEditModel::OpenMatch(AutocompleteMatch match,
       -1,  // don't yet know tab ID; set later if appropriate
       ClassifyPage(),
       elapsed_time_since_user_first_modified_omnibox,
-      match.inline_autocompletion.length(),
+      match.allowed_to_be_default_match ? match.inline_autocompletion.length() :
+          base::string16::npos,
       elapsed_time_since_last_change_to_default_match,
       (!popup_model()->IsOpen() || !pasted_text.empty()) ?
           fake_single_entry_result : result());

components/metrics/proto/omnibox_event.proto

@@ -55,8 +55,10 @@ message OmniboxEventProto {
   // The length of the inline autocomplete text in the omnibox.
   // The sum |typed_length| + |completed_length| gives the full length of the
   // user-visible text in the omnibox.
-  // This field is only set for inlineable suggestions selected at position 0
-  // (|selected_index| = 0) and will be omitted otherwise.
+  // This field is only set for suggestions that are allowed to be the default
+  // match and omitted otherwise.  The first suggestion is always allowed to
+  // be the default match.  (This is an enforced constraint.)  Hence, if
+  // |selected_index| == 0, then this field will always be set.
   optional int32 completed_length = 6;
 
   // The amount of time, in milliseconds, since the user first began modifying