Fix type punning in font_matcher_mac

It is undefined behavior in C++ to access memory of one type with
a pointer of another type. Use bit_cast to safely do it.

Bug: none
Change-Id: I170c81e0cc7dc5b7bcf63b0776758c4c65a748bf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2340180
Auto-Submit: Avi Drissman <avi@chromium.org>
Reviewed-by: Dominik Röttsches <drott@chromium.org>
Commit-Queue: Avi Drissman <avi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#796438}

third_party/blink/renderer/platform/fonts/mac/font_matcher_mac.mm

@@ -32,6 +32,8 @@
 #import <AppKit/AppKit.h>
 #import <Foundation/Foundation.h>
 #import <math.h>
+
+#include "base/bit_cast.h"
 #include "base/mac/foundation_util.h"
 #include "base/mac/scoped_cftyperef.h"
 #include "base/mac/scoped_nsobject.h"
@@ -59,17 +61,16 @@ static CGFloat toFontWeight(blink::FontSelectionValue font_weight) {
       0x3fe3d70a40000000,  // NSFontWeightBlack
   };
   if (font_weight <= 50 || font_weight >= 950)
-    return ns_font_weights[3];
+    return bit_cast<CGFloat>(ns_font_weights[3]);
 
   size_t select_weight = roundf(font_weight / 100) - 1;
   DCHECK_GE(select_weight, 0ul);
   DCHECK_LE(select_weight, base::size(ns_font_weights));
-  CGFloat* return_weight =
-      reinterpret_cast<CGFloat*>(&ns_font_weights[select_weight]);
-  return *return_weight;
-}
+  return bit_cast<CGFloat>(ns_font_weights[select_weight]);
 }
 
+}  // namespace
+
 namespace blink {
 
 const NSFontTraitMask SYNTHESIZED_FONT_TRAITS =