Simplify range mapping computation in SVGTextQuery/SVGInlineTextBox

Source/core/layout/svg/line/SVGInlineTextBox.cpp

Index: Source/core/layout/svg/line/SVGInlineTextBox.cpp
diff --git a/Source/core/layout/svg/line/SVGInlineTextBox.cpp b/Source/core/layout/svg/line/SVGInlineTextBox.cpp
index 654844c83a0ec105d46af77158d964fbde6a2d87..de9186e8268fe36ea6a9e0b48a1498e5028c6155 100644
--- a/Source/core/layout/svg/line/SVGInlineTextBox.cpp
+++ b/Source/core/layout/svg/line/SVGInlineTextBox.cpp
@@ -202,29 +202,17 @@ TextRun SVGInlineTextBox::constructTextRun(const ComputedStyle& style, const SVG
 
 bool SVGInlineTextBox::mapStartEndPositionsIntoFragmentCoordinates(const SVGTextFragment& fragment, int& startPosition, int& endPosition) const
 {
-    if (startPosition >= endPosition)
-        return false;
-
-    int offset = static_cast<int>(fragment.characterOffset) - start();
-    int length = static_cast<int>(fragment.length);
+    int fragmentOffsetInBox = static_cast<int>(fragment.characterOffset) - start();
 
-    if (startPosition >= offset + length || endPosition <= offset)
-        return false;
+    // Compute positions relative to the fragment.

[Erik Dahlström (inactive), 2015/04/01 14:04:20]

This used to leave startPosition and endPosition untouched in some cases, are
the callers of this method expecting that the values will now potentially always
change?

[fs, 2015/04/01 14:16:24]

The common pattern in callers are:

int startPos = fullStartPos;
int endPos = fullEndPos;
if (!mapStartEndPositionsIntoFragmentCoordinates(fragment, startPos, endPos))
    continue;
<use startPos, endPos>

the single user where that's not the case instead uses the returned bool (and a
"range empty" test). So, no, there's no caller that uses the values for anything
if false was returned.

+    startPosition -= fragmentOffsetInBox;
+    endPosition -= fragmentOffsetInBox;
 
-    if (startPosition < offset)
-        startPosition = 0;
-    else
-        startPosition -= offset;
+    // Intersect with the fragment range.
+    startPosition = std::max(startPosition, 0);
+    endPosition = std::min(endPosition, static_cast<int>(fragment.length));
 
-    if (endPosition > offset + length) {
-        endPosition = length;
-    } else {
-        ASSERT(endPosition >= offset);
-        endPosition -= offset;
-    }
-
-    ASSERT(startPosition < endPosition);
-    return true;
+    return startPosition < endPosition;
 }
 
 void SVGInlineTextBox::paintDocumentMarker(GraphicsContext*, const FloatPointWillBeLayoutPoint&, DocumentMarker*, const ComputedStyle&, const Font&, bool)