RenderTextHarfBuzz: Add support for multi line text selection.

ui/gfx/render_text_harfbuzz.h

Index: ui/gfx/render_text_harfbuzz.h
diff --git a/ui/gfx/render_text_harfbuzz.h b/ui/gfx/render_text_harfbuzz.h
index d3495255547ec684033a34122ad4be3b34259f86..72213433e9b57c02890f827a8e8e4e3861a092ab 100644
--- a/ui/gfx/render_text_harfbuzz.h
+++ b/ui/gfx/render_text_harfbuzz.h
@@ -193,7 +193,20 @@ class GFX_EXPORT RenderTextHarfBuzz : public RenderText {
   // Return the run index that contains the argument; or the length of the
   // |runs_| vector if argument exceeds the text length or width.
   size_t GetRunContainingCaret(const SelectionModel& caret);
-  size_t GetRunContainingXCoord(float x, float* offset) const;
+
+  // Returns the line index for the given argument. |text_y| is relative to
+  // the text bounds. Returns -1 if |text_y| is above the text and
+  // lines().size() if |text_y| is below it.
+  int GetLineContainingYCoord(float text_y);
+
+  // Returns the line segment index for the |line|, |text_x| pair. |text_x| is
+  // relative to text in the given line. Returns -1 if |text_x| is to the left
+  // of text in the line and |line|.segments.size() if it's to the right.
+  // |offset_relative_segment| will contain the offset of |text_x| relative to
+  // the start of the segment it is contained in.
+  int GetLineSegmentContainingXCoord(const internal::Line& line,
+                                     float text_x,
+                                     float* offset_relative_segment);
 
   // Given a |run|, returns the SelectionModel that contains the logical first
   // or last caret position inside (not at a boundary of) the run.