QVector: preserve capacity in clear()

This is what std::vector implementations usually do,
because it minimizes memory fragmentation and useless
allocations since no user will call clear() unless
she intends to append new data afterwards.

Fix calls to resize(0) that show how existing code
tried to work around the issue.

Adjust test. Port from QVERIFY(==) to QCOMPARE as a
drive-by.

[ChangeLog][QtCore][QVector] clear() now preserves
capacity. To shed capacity, call squeeze() or swap
with a default-constructed QVector object, see the
documentation for an example.

Change-Id: I9cebe611a97e027a89e821e64408a4741b31f1f6
Reviewed-by: Lars Knoll <lars.knoll@theqtcompany.com>

3 files changed, 3 insertions, 3 deletions

diff --git a/src/widgets/widgets/qmdiarea.cpp b/src/widgets/widgets/qmdiarea.cpp
index 2b734b603f..b42ebe7e48 100644
--- a/src/widgets/widgets/qmdiarea.cpp
+++ b/src/widgets/widgets/qmdiarea.cpp
@@ -516,7 +516,7 @@ QVector<QRect> MinOverlapPlacer::findMaxOverlappers(const QRect &domain, const Q
         if (overlap >= maxOverlap || maxOverlap == -1) {
             if (overlap > maxOverlap) {
                 maxOverlap = overlap;
-                result.resize(0);
+                result.clear();
             }
             result << srcRect;
         }
diff --git a/src/widgets/widgets/qmenubar.cpp b/src/widgets/widgets/qmenubar.cpp
index f15ce06e23..261ff0bca3 100644
--- a/src/widgets/widgets/qmenubar.cpp
+++ b/src/widgets/widgets/qmenubar.cpp
@@ -200,7 +200,7 @@ void QMenuBarPrivate::updateGeometries()
     if(itemsDirty) {
         for(int j = 0; j < shortcutIndexMap.size(); ++j)
             q->releaseShortcut(shortcutIndexMap.value(j));
-        shortcutIndexMap.resize(0); // faster than clear
+        shortcutIndexMap.clear();
         const int actionsCount = actions.count();
         shortcutIndexMap.reserve(actionsCount);
         for (int i = 0; i < actionsCount; i++)
diff --git a/src/widgets/widgets/qtextbrowser.cpp b/src/widgets/widgets/qtextbrowser.cpp
index d8a7b27d60..db66d39089 100644
--- a/src/widgets/widgets/qtextbrowser.cpp
+++ b/src/widgets/widgets/qtextbrowser.cpp
@@ -1141,7 +1141,7 @@ void QTextBrowser::clearHistory()
     d->forwardStack.clear();
     if (!d->stack.isEmpty()) {
         QTextBrowserPrivate::HistoryEntry historyEntry = d->stack.top();
-        d->stack.resize(0);
+        d->stack.clear();
         d->stack.push(historyEntry);
         d->home = historyEntry.url;
     }