Avoid unnecessary work in |RenderTextWin::UpdateLayout()| if there are no runs.

ui/gfx/render_text_win.cc

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/gfx/render_text_win.h"
 
 #include <algorithm>
 #include <map>
 
 #include "base/logging.h"
 #include "base/stl_util.h"
 #include "base/string_util.h"
+#include "base/win/scoped_hdc.h"
 #include "third_party/skia/include/core/SkTypeface.h"
 #include "ui/gfx/canvas.h"
 #include "ui/gfx/canvas_skia.h"
 
 namespace {
 
 // The maximum supported number of Uniscribe runs; a SCRIPT_ITEM is 8 bytes.
 // TODO(msw): Review memory use/failure? Max string length? Alternate approach?
 const int kGuessItems = 100;
 const int kMaxItems = 10000;
@@ skipping 286 matching lines @@
   size_t start = run->range.start();
   if (position == start)
     return true;
   return run->logical_clusters[position - start] !=
          run->logical_clusters[position - start - 1];
 }
 
 void RenderTextWin::UpdateLayout() {
   // TODO(msw): Skip complex processing if ScriptIsComplex returns false.
   ItemizeLogicalText();
-  HDC hdc = CreateCompatibleDC(NULL);
-  LayoutVisualText(hdc);
-  DeleteDC(hdc);
+  if (!runs_.empty()) {
+    base::win::ScopedCreateDC hdc(CreateCompatibleDC(NULL));

[msw, 2011/11/10 22:22:08]

You can optionally move this (and the runs_.empty check) into LayoutVisualText.
The arg is there in case re-using a DC or sharing one across
shaping/placement/drawing would help perf. But if this pattern is good, then the
arg is not needed.

[Alexei Svitkine (slow), 2011/11/11 14:53:48]

Done.

+    LayoutVisualText(hdc);
+  }
 }
 
 size_t RenderTextWin::IndexOfAdjacentGrapheme(size_t index, bool next) {
   size_t run_index = GetRunContainingPosition(index);
   internal::TextRun* run = run_index < runs_.size() ? runs_[run_index] : NULL;
   int start = run ? run->range.start() : 0;
   int length = run ? run->range.length() : text().length();
   int ch = index - start;
   WORD cluster = run ? run->logical_clusters[ch] : 0;
 
@@ skipping 334 matching lines @@
     Rect r(GetUpdatedCursorBounds());
     canvas->DrawRectInt(kCursorColor, r.x(), r.y(), r.width(), r.height());
   }
 }
 
 RenderText* RenderText::CreateRenderText() {
   return new RenderTextWin;
 }
 
 }  // namespace gfx