Uses and returns the fractional width in text eliding

On Mac, the width is repsented as CGFloat due to possible sub-pixel
rendering and extra kerning. We need to return the fractional widt,
instead of the integral width.

Some tests have been updated with the hack removed.

BUG=288987
TEST=new tests plus updating existing tests

Review URL: https://codereview.chromium.org/24883002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@227905 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 17 insertions, 0 deletions

diff --git a/ui/gfx/canvas.h b/ui/gfx/canvas.h
index 9aa7a0a..4470023 100644
--- a/ui/gfx/canvas.h
+++ b/ui/gfx/canvas.h
@@ -139,6 +139,15 @@ class GFX_EXPORT Canvas {
                             int line_height,
                             int flags);
 
+  // This is same as SizeStringInt except that fractional size is returned.
+  // See comment in GetStringWidthF for its usage.
+  static void SizeStringFloat(const base::string16& text,
+                              const FontList& font_list,
+                              float* width,
+                              float* height,
+                              int line_height,
+                              int flags);
+
   // Returns the number of horizontal pixels needed to display the specified
   // |text| with |font_list|.
   static int GetStringWidth(const base::string16& text,
@@ -146,6 +155,14 @@ class GFX_EXPORT Canvas {
   // Obsolete version.  Use the above version which takes FontList.
   static int GetStringWidth(const base::string16& text, const Font& font);
 
+  // This is same as GetStringWidth except that fractional width is returned.
+  // Use this method for the scenario that multiple string widths need to be
+  // summed up. This is because GetStringWidth returns the ceiled width and
+  // adding multiple ceiled widths could cause more precision loss for certain
+  // platform like Mac where the fractioal width is used.
+  static float GetStringWidthF(const base::string16& text,
+                               const FontList& font_list);
+
   // Returns the default text alignment to be used when drawing text on a
   // Canvas based on the directionality of the system locale language.
   // This function is used by Canvas::DrawStringInt when the text alignment