FontAccess: Move temporary structure declaration to Windows implementation

Small code cleanup: the temporary structure declared in the base
FontEnumerationCache class is moved to the Windows implementing class,
FontEnumerationCacheWin, because it's the only class that uses it.

Bug: 1043306
Change-Id: Ia6145f26a223d64a79920042c57e231eca575fe2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2422470
Commit-Queue: Olivier Yiptong <oyiptong@chromium.org>
Auto-Submit: Olivier Yiptong <oyiptong@chromium.org>
Reviewed-by: Joshua Bell <jsbell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#809343}

content/browser/font_access/font_enumeration_cache.h

@@ -73,9 +73,6 @@ class CONTENT_EXPORT FontEnumerationCache {
 
   bool IsFontEnumerationCacheValid() const;
 
-  // Protobuf structure temporarily used during cache construction and shared.
-  std::unique_ptr<blink::FontEnumerationTable> font_enumeration_table_;
-
   base::MappedReadOnlyRegion enumeration_cache_memory_;
   base::AtomicFlag enumeration_cache_built_;
   base::AtomicFlag enumeration_cache_build_started_;

content/browser/font_access/font_enumeration_cache_win.h

@@ -69,6 +69,9 @@ class CONTENT_EXPORT FontEnumerationCacheWin : public FontEnumerationCache {
   Microsoft::WRL::ComPtr<IDWriteFontCollection> collection_;
   uint32_t outstanding_family_results_ = 0;
 
+  // Protobuf structure temporarily used during cache construction and shared.
+  std::unique_ptr<blink::FontEnumerationTable> font_enumeration_table_;
+
   std::map<HRESULT, unsigned> enumeration_errors_;
   std::unique_ptr<base::ElapsedTimer> enumeration_timer_;