Change Font::offsetForPositionForComplexText to use CachingWordShapeIterator

Source/platform/fonts/shaping/HarfBuzzShaper.cpp

Index: Source/platform/fonts/shaping/HarfBuzzShaper.cpp
diff --git a/Source/platform/fonts/shaping/HarfBuzzShaper.cpp b/Source/platform/fonts/shaping/HarfBuzzShaper.cpp
index 22e181f679e9dc53fcc06f0451fa188630533f70..cf38fc428c40509d0026a5b7fe517f2878897fb8 100644
--- a/Source/platform/fonts/shaping/HarfBuzzShaper.cpp
+++ b/Source/platform/fonts/shaping/HarfBuzzShaper.cpp
@@ -39,6 +39,7 @@
 #include "platform/fonts/Font.h"
 #include "platform/fonts/GlyphBuffer.h"
 #include "platform/fonts/UTF16TextIterator.h"
+#include "platform/fonts/shaping/CachingWordShapeIterator.h"
 #include "platform/fonts/shaping/HarfBuzzFace.h"
 #include "platform/text/TextBreakIterator.h"
 #include "wtf/Compiler.h"
@@ -441,6 +442,39 @@ FloatRect ShapeResult::selectionRect(Vector<RefPtr<ShapeResult>>& results,
     return FloatRect(point.x() + toX, point.y(), fromX - toX, height);
 }
 
+int ShapeResult::offsetForPosition(CachingWordShapeIterator& iterator,
+    const TextRun& run, float targetX)
+{
+    RefPtr<ShapeResult> wordResult;
+    unsigned totalOffset;
+    if (run.rtl()) {
+        totalOffset = run.length();
+        while (iterator.next(&wordResult)) {
+            if (!wordResult)
+                continue;
+            totalOffset -= wordResult->numCharacters();
+            if (targetX >= 0 && targetX <= wordResult->width()) {
+                int offsetForWord = wordResult->offsetForPosition(targetX);
+                return totalOffset + offsetForWord;
+            }
+            targetX -= wordResult->width();
+        }
+    } else {
+        totalOffset = 0;
+        while (iterator.next(&wordResult)) {
+            if (!wordResult)
+                continue;
+            int offsetForWord = wordResult->offsetForPosition(targetX);
+            ASSERT(offsetForWord >= 0);
+            totalOffset += offsetForWord;
+            if (targetX >= 0 && targetX <= wordResult->width())
+                return totalOffset;
+            targetX -= wordResult->width();
+        }
+    }
+    return totalOffset;
+}
+
 int ShapeResult::offsetForPosition(float targetX)
 {
     int charactersSoFar = 0;