Instant: refactor code intended to prevent extra work.

current symptoms:
- when you send two OnChanges in a row, the second one will get the a blank |suggested_text|.
- if you type alaska, the suggestion is "alaska air". Pressing space returns a blank |suggested_text|.

fix:
- return last suggestion. Also consolidate two points in the code where we tried to prevent Update from doing extra work.

BUG=64245
TEST=manual (see bug and above)

Review URL: http://codereview.chromium.org/5330003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@67206 0039d316-1c4b-4281-b951-d872f2087c98

3 files changed, 27 insertions, 22 deletions

diff --git a/chrome/browser/instant/instant_controller.cc b/chrome/browser/instant/instant_controller.cc
index 5f7d4b6..c1b32b7 100644
--- a/chrome/browser/instant/instant_controller.cc
+++ b/chrome/browser/instant/instant_controller.cc
@@ -161,6 +161,8 @@ void InstantController::Update(TabContentsWrapper* tab_contents,
                                const string16& user_text,
                                bool verbatim,
                                string16* suggested_text) {
+  suggested_text->clear();
+
   if (tab_contents != tab_contents_)
     DestroyPreviewContents();
 
@@ -170,20 +172,6 @@ void InstantController::Update(TabContentsWrapper* tab_contents,
   commit_on_mouse_up_ = false;
   last_transition_type_ = match.transition;
 
-  const TemplateURL* template_url = GetTemplateURL(match);
-  TemplateURLID template_url_id = template_url ? template_url->id() : 0;
-  // Verbatim only makes sense if the search engines supports instant.
-  bool real_verbatim = template_url_id ? verbatim : false;
-
-  if (loader_manager_.get()) {
-    InstantLoader* active_loader = loader_manager_->active_loader();
-    if (active_loader->url() == url &&
-        active_loader->template_url_id() == template_url_id &&
-        (!template_url_id || active_loader->verbatim() == real_verbatim)) {
-      return;
-    }
-  }
-
   if (url.is_empty() || !url.is_valid() || !ShouldShowPreviewFor(match)) {
     DestroyPreviewContents();
     return;
@@ -195,6 +183,11 @@ void InstantController::Update(TabContentsWrapper* tab_contents,
   if (!is_active_)
     delegate_->PrepareForInstant();
 
+  const TemplateURL* template_url = GetTemplateURL(match);
+  TemplateURLID template_url_id = template_url ? template_url->id() : 0;
+  // Verbatim only makes sense if the search engines supports instant.
+  bool real_verbatim = template_url_id ? verbatim : false;
+
   if (ShouldUpdateNow(template_url_id, match.destination_url)) {
     UpdateLoader(template_url, match.destination_url, match.transition,
                  user_text, real_verbatim, suggested_text);
diff --git a/chrome/browser/instant/instant_loader.cc b/chrome/browser/instant/instant_loader.cc
index 9ef682d..90f6689 100644
--- a/chrome/browser/instant/instant_loader.cc
+++ b/chrome/browser/instant/instant_loader.cc
@@ -407,17 +407,25 @@ void InstantLoader::Update(TabContentsWrapper* tab_contents,
                            const string16& user_text,
                            bool verbatim,
                            string16* suggested_text) {
-  if (url_ == url && verbatim == verbatim_)
+  // Strip leading ?.
+  string16 new_user_text =
+      !user_text.empty() && (UTF16ToWide(user_text)[0] == L'?') ?
+      user_text.substr(1) : user_text;
+
+  // If state hasn't changed, just reuse the last suggestion.
+  if (url_ == url && verbatim == verbatim_ && user_text_ == new_user_text &&
+      last_transition_type_ == transition_type) {
+    suggested_text->assign(last_suggestion_);
     return;
+  }
 
   DCHECK(!url.is_empty() && url.is_valid());
 
   last_transition_type_ = transition_type;
   url_ = url;
-  // Strip leading ?.
-  user_text_ = !user_text.empty() && (UTF16ToWide(user_text)[0] == L'?') ?
-      user_text.substr(1) : user_text;
+  user_text_ = new_user_text;
   verbatim_ = verbatim;
+  last_suggestion_.clear();
 
   bool created_preview_contents;
   if (preview_contents_.get() == NULL) {
@@ -480,7 +488,8 @@ void InstantLoader::Update(TabContentsWrapper* tab_contents,
           complete_suggested_text_lower.size() > user_text_lower.size() &&
           !complete_suggested_text_lower.compare(0, user_text_lower.size(),
                                                  user_text_lower)) {
-        *suggested_text = complete_suggested_text_.substr(user_text_.size());
+        *suggested_text = last_suggestion_ =
+            complete_suggested_text_.substr(user_text_.size());
       }
     } else {
       // Load the instant URL. We don't reflect the url we load in url() as
@@ -616,6 +625,7 @@ void InstantLoader::SetCompleteSuggestedText(
   string16 user_text_lower = l10n_util::ToLower(user_text_);
   string16 complete_suggested_text_lower = l10n_util::ToLower(
       complete_suggested_text);
+  last_suggestion_.clear();
   if (user_text_lower.compare(0, user_text_lower.size(),
                               complete_suggested_text_lower,
                               0, user_text_lower.size())) {
@@ -626,9 +636,8 @@ void InstantLoader::SetCompleteSuggestedText(
   }
 
   complete_suggested_text_ = complete_suggested_text;
-  delegate_->SetSuggestedTextFor(
-      this,
-      complete_suggested_text_.substr(user_text_.size()));
+  last_suggestion_ = complete_suggested_text_.substr(user_text_.size());
+  delegate_->SetSuggestedTextFor(this, last_suggestion_);
 }
 
 void InstantLoader::PreviewPainted() {
diff --git a/chrome/browser/instant/instant_loader.h b/chrome/browser/instant/instant_loader.h
index f19b239..7527bf4 100644
--- a/chrome/browser/instant/instant_loader.h
+++ b/chrome/browser/instant/instant_loader.h
@@ -162,6 +162,9 @@ class InstantLoader : public NotificationObserver {
   // The latest suggestion from the page.
   string16 complete_suggested_text_;
 
+  // The latest suggestion (suggested text less the user text).
+  string16 last_suggestion_;
+
   // See description above setter.
   gfx::Rect omnibox_bounds_;