Change HarfBuzz selectionRect rounding to match simple text version

Source/platform/fonts/harfbuzz/HarfBuzzShaper.cpp

 /*
  * Copyright (c) 2012 Google Inc. All rights reserved.
  * Copyright (C) 2013 BlackBerry Limited. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
@@ skipping 16 matching lines @@
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #include "config.h"
 #include "platform/fonts/harfbuzz/HarfBuzzShaper.h"
 
 #include "RuntimeEnabledFeatures.h"
 #include "hb.h"
+#include "platform/LayoutUnit.h"
 #include "platform/fonts/Character.h"
 #include "platform/fonts/Font.h"
 #include "platform/fonts/harfbuzz/HarfBuzzFace.h"
 #include "platform/text/SurrogatePairAwareTextIterator.h"
 #include "platform/text/TextBreakIterator.h"
 #include "wtf/Compiler.h"
 #include "wtf/MathExtras.h"
 #include "wtf/unicode/Unicode.h"
 #include <unicode/normlzr.h>
 #include <unicode/uchar.h>
@@ skipping 1057 matching lines @@
             currentX += m_harfBuzzRuns[i]->width();
     }
 
     // The position in question might be just after the text.
     if (!foundFromX)
         fromX = 0;
     if (!foundToX)
         toX = m_run.rtl() ? 0 : m_totalWidth;
 
     // Using floorf() and roundf() as the same as mac port.
-    if (fromX < toX)
-        return FloatRect(floorf(point.x() + fromX), point.y(), roundf(toX - fromX), height);
-    return FloatRect(floorf(point.x() + toX), point.y(), roundf(fromX - toX), height);
+    // Use LayoutUnit::epsilon() to ensure that values that cannot be stored as
+    // an integer are floored to n and not n-1 due to floating point imprecision.
+    if (fromX < toX) {
+        float pixelAlignedX = floorf(point.x() + fromX + LayoutUnit::epsilon());
+        return FloatRect(floorf(point.x() + fromX),
+            point.y(),
+            roundf(point.x() + toX) - pixelAlignedX,
+            height);
+    }
+
+    float pixelAlignedX = floorf(point.x() + toX + LayoutUnit::epsilon());
+    return FloatRect(floorf(point.x() + toX),
+        point.y(),
+        roundf(point.x() + fromX) - pixelAlignedX,
+        height);
 }
 
 } // namespace WebCore