Track tail of strike cache

Change-Id: Ic5d5ae5d4c45d0bc5b82dd2257752184a8b529d0
Reviewed-on: https://skia-review.googlesource.com/123935
Commit-Queue: Herb Derby <herb@google.com>
Commit-Queue: Ben Wagner <bungeman@google.com>
Auto-Submit: Herb Derby <herb@google.com>
Reviewed-by: Ben Wagner <bungeman@google.com>

src/core/SkStrikeCache.cpp

@@ -342,16 +342,6 @@ void SkStrikeCache::forEachStrike(std::function<void(const SkGlyphCache&)> visit
     }
 }
 
-SkStrikeCache::Node* SkStrikeCache::internalGetTail() const {
-    Node* node = fHead;
-    if (node) {
-        while (node->fNext) {
-            node = node->fNext;
-        }
-    }
-    return node;
-}
-
 size_t SkStrikeCache::internalPurge(size_t minBytesNeeded) {
     this->validate();
 
@@ -416,6 +406,10 @@ void SkStrikeCache::internalAttachToHead(Node* node) {
     }
     fHead = node;
 
+    if (fTail == nullptr) {
+        fTail = node;
+    }
+
     fCacheCount += 1;
     fTotalMemoryUsed += node->fCache.getMemoryUsed();
 }
@@ -432,6 +426,8 @@ void SkStrikeCache::internalDetachCache(Node* node) {
     }
     if (node->fNext) {
         node->fNext->fPrev = node->fPrev;
+    } else {
+        fTail = node->fPrev;
     }
     node->fPrev = node->fNext = nullptr;
 }

src/core/SkStrikeCache.h

@@ -144,7 +144,7 @@ private:
 
     // The following methods can only be called when mutex is already held.
     Node* internalGetHead() const { return fHead; }
-    Node* internalGetTail() const;
+    Node* internalGetTail() const { return fTail; }
     void internalDetachCache(Node*);
     void internalAttachToHead(Node*);
 
@@ -157,6 +157,7 @@ private:
 
     mutable SkSpinlock fLock;
     Node*              fHead{nullptr};
+    Node*              fTail{nullptr};
     size_t             fTotalMemoryUsed{0};
     size_t             fCacheSizeLimit{SK_DEFAULT_FONT_CACHE_LIMIT};
     int32_t            fCacheCountLimit{SK_DEFAULT_FONT_CACHE_COUNT_LIMIT};