RenderTextHarfBuzz: Add support for multi line text selection.

ui/gfx/render_text_harfbuzz.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_GFX_RENDER_TEXT_HARFBUZZ_H_
 #define UI_GFX_RENDER_TEXT_HARFBUZZ_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 175 matching lines @@
   // Specify the width of a glyph for test. The width of glyphs is very
   // platform-dependent and environment-dependent. Otherwise multiline test
   // will become really flaky.
   void set_glyph_width_for_test(float test_width) {
     glyph_width_for_test_ = test_width;
   }
 
   // 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.
   // The returned value represents a cursor/caret position without a selection.
   SelectionModel FirstSelectionModelInsideRun(
       const internal::TextRunHarfBuzz* run);
   SelectionModel LastSelectionModelInsideRun(
       const internal::TextRunHarfBuzz* run);
 
   // Break the text into logical runs and populate the visual <-> logical maps
@@ skipping 57 matching lines @@
 
   // Fixed width of glyphs. This should only be set in test environments.
   float glyph_width_for_test_;
 
   DISALLOW_COPY_AND_ASSIGN(RenderTextHarfBuzz);
 };
 
 }  // namespace gfx
 
 #endif  // UI_GFX_RENDER_TEXT_HARFBUZZ_H_