RenderTextHarfBuzz: Add support for multi line text selection.

ui/gfx/render_text.h

Index: ui/gfx/render_text.h
diff --git a/ui/gfx/render_text.h b/ui/gfx/render_text.h
index 7e0b48310116e1fa2cf8ac004389c6bae197a084..ecbb26c20da16cda9808b5443bacaea9595b465d 100644
--- a/ui/gfx/render_text.h
+++ b/ui/gfx/render_text.h
@@ -209,14 +209,19 @@ void ApplyRenderParams(const FontRenderParams& params,
 // for rendering and translation between logical and visual data.
 class GFX_EXPORT RenderText {
  public:
-// The character used for displaying obscured text.
-// TODO(benrg): GTK uses the first of U+25CF, U+2022, U+2731, U+273A, '*'
-// that's available in the font (find_invisible_char() in gtkentry.c).
-// Use a bullet character on Mac.
 #if defined(OS_MACOSX)
+  // The character used for displaying obscured text.
+  // TODO(benrg): GTK uses the first of U+25CF, U+2022, U+2731, U+273A, '*'
+  // that's available in the font (find_invisible_char() in gtkentry.c).
+  // Use a bullet character on Mac.
   static constexpr base::char16 kPasswordReplacementChar = 0x2022;
+
+  // On Mac, while selecting text if the cursor is outside the vertical text
+  // bounds, drag to the end of the text.
+  static constexpr bool kDragToEndIfOutsideVerticalBounds = true;
 #else
   static constexpr base::char16 kPasswordReplacementChar = '*';
+  static constexpr bool kDragToEndIfOutsideVerticalBounds = false;
 #endif
 
   virtual ~RenderText();
@@ -412,10 +417,11 @@ class GFX_EXPORT RenderText {
   }
   base::i18n::TextDirection GetDisplayTextDirection();
 
-  // Returns the visual movement direction corresponding to the logical end
-  // of the text, considering only the dominant direction returned by
-  // |GetDisplayTextDirection()|, not the direction of a particular run.
+  // Returns the visual movement direction corresponding to the logical
+  // end/beginning of the text, considering only the dominant direction returned
+  // by |GetDisplayTextDirection()|, not the direction of a particular run.
   VisualCursorDirection GetVisualDirectionOfLogicalEnd();
+  VisualCursorDirection GetVisualDirectionOfLogicalBeginning();
 
   // Returns the text used to display, which may be obscured, truncated or
   // elided. The subclass may compute elided text on the fly, or use
@@ -473,6 +479,7 @@ class GFX_EXPORT RenderText {
   // is longer than the textfield. Subsequent text, cursor, or bounds changes
   // may invalidate returned values. Note that |caret| must be placed at
   // grapheme boundary, i.e. caret.caret_pos() must be a cursorable position.
+  // Note: This function does not support multiline currently.
   Rect GetCursorBounds(const SelectionModel& caret, bool insert_mode);
 
   // Compute the current cursor bounds, panning the text to show the cursor in
@@ -595,6 +602,12 @@ class GFX_EXPORT RenderText {
   // The returned value represents a cursor/caret position without a selection.
   SelectionModel EdgeSelectionModel(VisualCursorDirection direction);
 
+  // Get the selection model corresponding to visual text ends for the given
+  // |line|.
+  // The returned value represents a cursor/caret position without a selection.
+  SelectionModel LineSelectionModel(const internal::Line& line,
+                                    gfx::VisualCursorDirection direction);
+
   // Sets the selection model, the argument is assumed to be valid.
   virtual void SetSelectionModel(const SelectionModel& model);
 
@@ -640,14 +653,10 @@ class GFX_EXPORT RenderText {
   void ApplyCompositionAndSelectionStyles();
   void UndoCompositionAndSelectionStyles();
 
-  // Convert points from the text space to the view space and back. Handles the
-  // display area, display offset, application LTR/RTL mode and multiline.
-  Point ToTextPoint(const Point& point);
+  // Convert points from the text space to the view space. Handles the display
+  // area, display offset, application LTR/RTL mode and multiline.
   Point ToViewPoint(const Point& point);
 
-  // Convert a text space x-coordinate range to rects in view space.
-  std::vector<Rect> TextBoundsToViewBounds(const Range& x);
-
   // Get the alignment, resolving ALIGN_TO_HEAD with the current text direction.
   HorizontalAlignment GetCurrentHorizontalAlignment();