Do not break lines when width is not specified.

ui/views/controls/label.cc

 // Copyright (c) 2012 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/views/controls/label.h"
 
 #include <algorithm>
 #include <cmath>
 #include <limits>
 #include <vector>
@@ skipping 481 matching lines @@
     }
   }
 
   focus_bounds.Inset(-kFocusBorderPadding, -kFocusBorderPadding);
   focus_bounds.Intersect(GetLocalBounds());
   return focus_bounds;
 }
 
 std::vector<base::string16> Label::GetLinesForWidth(int width) const {
   std::vector<base::string16> lines;
-  const gfx::WordWrapBehavior wrap =
-      allow_character_break_ ? gfx::WRAP_LONG_WORDS : gfx::TRUNCATE_LONG_WORDS;
-  gfx::ElideRectangleText(render_text_->GetDisplayText(), font_list(), width,
-                          std::numeric_limits<int>::max(), wrap, &lines);
+  // |width| can be 0 when getting the default text size, in that case
+  // the ideal lines (i.e. broken at newline characters) are wanted.
+  if (width <= 0) {
+    base::SplitString(render_text_->GetDisplayText(), '\n', &lines);
+  } else {
+    const gfx::WordWrapBehavior wrap = allow_character_break_
+                                           ? gfx::WRAP_LONG_WORDS
+                                           : gfx::TRUNCATE_LONG_WORDS;
+    gfx::ElideRectangleText(render_text_->GetDisplayText(), font_list(), width,
+                            std::numeric_limits<int>::max(), wrap, &lines);
+  }
   return lines;
 }
 
 gfx::Size Label::GetTextSize() const {
   gfx::Size size;
   if (text().empty()) {
     size = gfx::Size(0, std::max(line_height(), font_list().GetHeight()));
   } else if (!multi_line() ||
              (render_text_->MultilineSupported() && !allow_character_break_)) {
     // Cancel the display rect of |render_text_|. The display rect may be
@@ skipping 58 matching lines @@
 }
 
 bool Label::ShouldShowDefaultTooltip() const {
   const gfx::Size text_size = GetTextSize();
   const gfx::Size size = GetContentsBounds().size();
   return !obscured() && (text_size.width() > size.width() ||
                          (multi_line() && text_size.height() > size.height()));
 }
 
 }  // namespace views