Fix Font::TabWidth not to return -NaN

This patch fixes the |float| variation of |Font::TabWidth|
not to return -NaN by adding the same guard as its
|LayoutUnit| variation.

Bug: 1002999
Change-Id: I4fc1fdb233b4156a425c92d97f7f9444be527d12
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1798070Reviewed-by: Emil A Eklund <eae@chromium.org>
Commit-Queue: Emil A Eklund <eae@chromium.org>
Commit-Queue: Koji Ishii <kojii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#695829}

third_party/blink/renderer/platform/fonts/font.cc

@@ -550,6 +550,24 @@ void Font::ExpandRangeToIncludePartialGlyphs(const TextRun& text_run,
   buffer.ExpandRangeToIncludePartialGlyphs(from, to);
 }
 
+float Font::TabWidth(const SimpleFontData* font_data,
+                     const TabSize& tab_size,
+                     float position) const {
+  float base_tab_width = TabWidth(font_data, tab_size);
+  if (!base_tab_width)
+    return GetFontDescription().LetterSpacing();
+
+  float distance_to_tab_stop = base_tab_width - fmodf(position, base_tab_width);
+
+  // Let the minimum width be the half of the space width so that it's always
+  // recognizable.  if the distance to the next tab stop is less than that,
+  // advance an additional tab stop.
+  if (distance_to_tab_stop < font_data->SpaceWidth() / 2)
+    distance_to_tab_stop += base_tab_width;
+
+  return distance_to_tab_stop;
+}
+
 LayoutUnit Font::TabWidth(const TabSize& tab_size, LayoutUnit position) const {
   const SimpleFontData* font_data = PrimaryFont();
   if (!font_data)

third_party/blink/renderer/platform/fonts/font.h

@@ -276,21 +276,6 @@ inline float Font::TabWidth(const SimpleFontData* font_data,
   return base_tab_width ? base_tab_width : GetFontDescription().LetterSpacing();
 }
 
-inline float Font::TabWidth(const SimpleFontData* font_data,
-                            const TabSize& tab_size,
-                            float position) const {
-  float base_tab_width = TabWidth(font_data, tab_size);
-  float distance_to_tab_stop = base_tab_width - fmodf(position, base_tab_width);
-
-  // Let the minimum width be the half of the space width so that it's always
-  // recognizable.  if the distance to the next tab stop is less than that,
-  // advance an additional tab stop.
-  if (distance_to_tab_stop < font_data->SpaceWidth() / 2)
-    distance_to_tab_stop += base_tab_width;
-
-  return distance_to_tab_stop;
-}
-
 }  // namespace blink
 
 #endif

third_party/blink/renderer/platform/fonts/font_test.cc

@@ -9,6 +9,7 @@
 #include "third_party/blink/renderer/platform/fonts/text_run_paint_info.h"
 #include "third_party/blink/renderer/platform/testing/font_test_helpers.h"
 #include "third_party/blink/renderer/platform/testing/unit_test_helpers.h"
+#include "third_party/blink/renderer/platform/text/tab_size.h"
 #include "third_party/blink/renderer/platform/text/text_run.h"
 
 using blink::test::CreateTestFont;
@@ -86,4 +87,12 @@ TEST_F(FontTest, ExpandRange) {
   EXPECT_EQ(GetExpandedRange("tneiciffe", false, 0, 9), Vector<int>({0, 9}));
 }
 
+TEST_F(FontTest, TabWidthZero) {
+  Font font =
+      CreateTestFont("Ahem", test::PlatformTestDataPath("Ahem.woff"), 0);
+  TabSize tab_size(8);
+  EXPECT_EQ(font.TabWidth(tab_size, .0f), .0f);
+  EXPECT_EQ(font.TabWidth(tab_size, LayoutUnit()), LayoutUnit());
+}
+
 }  // namespace blink