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

ui/gfx/render_text_win.cc

Index: ui/gfx/render_text_win.cc
===================================================================
--- ui/gfx/render_text_win.cc	(revision 109436)
+++ ui/gfx/render_text_win.cc	(working copy)
@@ -10,6 +10,7 @@
 #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"
@@ -316,9 +317,10 @@
 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) {