Reduce 4 byte from HarfBuzzRunGlyphData for Windows

This patch makes |HarfBuzzRunGlyphData| four byte smaller by omitting structure
alignment padding to reduce memory usage for Windows.

Note: Linux doesn't insert padding after |unit16_t|.

In rude estimation, we can reduce:
  number_of_character_in_page × 4 byte
per page.

Example: https://en.wikipedia.org
document.body.innerText.length = 9681
Thus, we can reduce 38,724 byte.


Before this patch:
   +----------+----------+
+0 | utin16_t | padding  |
   +----------+----------+
+4 | bit field           |
   +----------+----------+
+8 | float advance       |
   +----------+----------+
   ...
sizeof(HarfBuzzRunGlyphData)==20

After this patch:
   +----------+----------+
+0 | bit field           |
   +----------+----------+
+4 | float advance       |
   +----------+----------+
   ...
sizeof(HarfBuzzRunGlyphData)==16


Bug: 965564
Change-Id: I73cae1096d74168ead1e2e48251dc2d50597e7e8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1627832
Commit-Queue: Yoshifumi Inoue <yosin@chromium.org>
Auto-Submit: Yoshifumi Inoue <yosin@chromium.org>
Reviewed-by: Emil A Eklund <eae@chromium.org>
Cr-Commit-Position: refs/heads/master@{#662974}

third_party/blink/renderer/platform/fonts/shaping/shape_result.cc

@@ -55,8 +55,8 @@ constexpr unsigned HarfBuzzRunGlyphData::kMaxCharacterIndex;
 constexpr unsigned HarfBuzzRunGlyphData::kMaxGlyphs;
 
 struct SameSizeAsHarfBuzzRunGlyphData {
-  uint16_t unsigned_int16;
-  unsigned bit_fields : 2;
+  unsigned glyph : 16;
+  unsigned char_index_and_bit_field : 16;
   float advance;
   FloatSize offset;
 };

third_party/blink/renderer/platform/fonts/shaping/shape_result_inline_headers.h

@@ -51,7 +51,7 @@ struct HarfBuzzRunGlyphData {
   static constexpr unsigned kMaxCharacterIndex = (1 << kCharacterIndexBits) - 1;
   static constexpr unsigned kMaxGlyphs = 1 << kCharacterIndexBits;
 
-  uint16_t glyph;
+  unsigned glyph : 16;
   unsigned character_index : kCharacterIndexBits;
   unsigned safe_to_break_before : 1;