Let TabCountProvider obtain tab count from both TabModels

This CL adds a package-protected API getTabCount(boolean isIncognito)
to TabCountProvider. This API is needed because the
IncognitoToggleTabLayout need the count for normal model even when the
current model is incognito. As is, TabCountProvider only
provides current model count.

Bug: 935818
Change-Id: I0b6f2184226c74820ef6b6e00d7a04118d07d6e0
Reviewed-on: https://chromium-review.googlesource.com/c/1488021
Commit-Queue: Mei Liang <meiliang@chromium.org>
Reviewed-by: Wei-Yin Chen (陳威尹) <wychen@chromium.org>
Reviewed-by: Yusuf Ozuysal <yusufo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#635425}

chrome/android/java/src/org/chromium/chrome/browser/toolbar/IncognitoToggleTabLayout.java

@@ -101,7 +101,8 @@ public class IncognitoToggleTabLayout extends TabLayout implements TabCountObser
         mTabModelSelector.addObserver(mTabModelSelectorObserver);
         setStateBasedOnModel();
 
-        mTabSwitcherDrawable.updateForTabCount(mTabModelSelector.getModel(false).getCount(), false);
+        assert mTabCountProvider != null;
+        mTabSwitcherDrawable.updateForTabCount(mTabCountProvider.getTabCount(false), false);
     }
 
     public void setTabCountProvider(TabCountProvider tabCountProvider) {

chrome/android/java/src/org/chromium/chrome/browser/toolbar/TabCountProvider.java

@@ -164,4 +164,10 @@ public class TabCountProvider {
             observer.onTabCountChanged(tabCount, isIncognito);
         }
     }
+
+    protected int getTabCount(boolean isIncognito) {
+        return mTabModelSelector.getTabModelFilterProvider()
+                .getTabModelFilter(isIncognito)
+                .getCount();
+    }
 }