Get rid of a mutable member from FontDescription

FontDescription has a mutable bit field subpixel_ascent_descent_ that
can be modified via a const method. This patch removes the mutable
keyword and changes the callers so that FontDescription no longer has
mutable fields, and the code maintainability is improved.

Change-Id: I53fab83b3a8c00e2827aa19b0ba640bb59765fda
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2145072Reviewed-by: Fernando Serboncini <fserb@chromium.org>
Reviewed-by: Koji Ishii <kojii@chromium.org>
Commit-Queue: Xiaocheng Hu <xiaochengh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#759798}

third_party/blink/renderer/modules/canvas/canvas2d/canvas_rendering_context_2d.cc

@@ -846,7 +846,6 @@ void CanvasRenderingContext2D::DrawTextInternal(
     return;
 
   const Font& font = AccessFont();
-  font.GetFontDescription().SetSubpixelAscentDescent(true);
   const SimpleFontData* font_data = font.PrimaryFont();
   DCHECK(font_data);
   if (!font_data)

third_party/blink/renderer/modules/canvas/canvas2d/canvas_rendering_context_2d_state.cc

@@ -254,8 +254,10 @@ void CanvasRenderingContext2DState::ClipPath(
 }
 
 void CanvasRenderingContext2DState::SetFont(
-    const FontDescription& font_description,
+    const FontDescription& passed_font_description,
     FontSelector* selector) {
+  FontDescription font_description = passed_font_description;
+  font_description.SetSubpixelAscentDescent(true);
   font_ = Font(font_description, selector);
   realized_font_ = true;
   if (selector)

third_party/blink/renderer/modules/canvas/offscreencanvas2d/offscreen_canvas_rendering_context_2d.cc

@@ -510,8 +510,6 @@ void OffscreenCanvasRenderingContext2D::DrawTextInternal(
     return;
 
   const Font& font = AccessFont();
-  font.GetFontDescription().SetSubpixelAscentDescent(true);
-
   const SimpleFontData* font_data = font.PrimaryFont();
   DCHECK(font_data);
   if (!font_data)

third_party/blink/renderer/platform/fonts/font_description.h

@@ -328,7 +328,7 @@ class PLATFORM_EXPORT FontDescription {
   }
   static bool SubpixelPositioning() { return use_subpixel_text_positioning_; }
 
-  void SetSubpixelAscentDescent(bool sp) const {
+  void SetSubpixelAscentDescent(bool sp) {
     fields_.subpixel_ascent_descent_ = sp;
   }
 
@@ -420,7 +420,7 @@ class PLATFORM_EXPORT FontDescription {
     unsigned typesetting_features_ : 3;
     unsigned variant_numeric_ : 8;
     unsigned variant_east_asian_ : 6;
-    mutable unsigned subpixel_ascent_descent_ : 1;
+    unsigned subpixel_ascent_descent_ : 1;
     unsigned font_optical_sizing_ : 1;
   };