tiny_skia: Add a capacity limit to GlyphCache

 * Trim the cache if `recently_used` size reaches the limit, even if a
   trim interval hasn't passed.
 * Shrink `entries` and `recently_used` to the limit when trimming.

Signed-off-by: Mohammad AlSaleh <CE.Mohammad.AlSaleh@gmail.com>

tiny_skia/src/text.rs

@@ -258,6 +258,7 @@ struct GlyphCache {
 
 impl GlyphCache {
     const TRIM_INTERVAL: usize = 300;
+    const CAPACITY_LIMIT:usize = 16*1024;
 
     fn new() -> Self {
         GlyphCache::default()
@@ -344,12 +345,15 @@ impl GlyphCache {
     }
 
     pub fn trim(&mut self) {
-        if self.trim_count > Self::TRIM_INTERVAL {
+        if self.trim_count > Self::TRIM_INTERVAL || self.recently_used.len() >= Self::CAPACITY_LIMIT {
             self.entries
                 .retain(|key, _| self.recently_used.contains(key));
 
             self.recently_used.clear();
 
+            self.entries.shrink_to(Self::CAPACITY_LIMIT);
+            self.recently_used.shrink_to(Self::CAPACITY_LIMIT);
+
             self.trim_count = 0;
         } else {
             self.trim_count += 1;