Bug 846215 - separate content and chrome word cache metrics. r=taras

gfx/thebes/gfxFont.cpp

@@ -2449,13 +2449,19 @@ gfxFont::GetShapedWord(gfxContext *aContext,
     }
     gfxShapedWord *sw = entry->mShapedWord;
 
+    bool isContent = !mStyle.systemFont;
+
     if (sw) {
         sw->ResetAge();
-        Telemetry::Accumulate(Telemetry::WORD_CACHE_HITS, aLength);
+        Telemetry::Accumulate((isContent ? Telemetry::WORD_CACHE_HITS_CONTENT :
+                                   Telemetry::WORD_CACHE_HITS_CHROME),
+                              aLength);
         return sw;
     }
 
-    Telemetry::Accumulate(Telemetry::WORD_CACHE_MISSES, aLength);
+    Telemetry::Accumulate((isContent ? Telemetry::WORD_CACHE_MISSES_CONTENT :
+                               Telemetry::WORD_CACHE_MISSES_CHROME),
+                          aLength);
     sw = entry->mShapedWord = gfxShapedWord::Create(aText, aLength,
                                                     aRunScript,
                                                     aAppUnitsPerDevUnit,

toolkit/components/telemetry/Histograms.json

@@ -485,17 +485,29 @@
     "kind": "flag",
     "description": "Was the disk startup cache file detected as invalid"
   },
-  "WORD_CACHE_HITS": {
+  "WORD_CACHE_HITS_CONTENT": {
     "kind": "exponential",
     "high": "256",
     "n_buckets": 30,
-    "description": "Word cache hits (chars)"
+    "description": "Word cache hits, content text (chars)"
   },
-  "WORD_CACHE_MISSES": {
+  "WORD_CACHE_HITS_CHROME": {
     "kind": "exponential",
     "high": "256",
     "n_buckets": 30,
-    "description": "Word cache misses (chars)"
+    "description": "Word cache hits, chrome text (chars)"
+  },
+  "WORD_CACHE_MISSES_CONTENT": {
+    "kind": "exponential",
+    "high": "256",
+    "n_buckets": 30,
+    "description": "Word cache misses, content text (chars)"
+  },
+  "WORD_CACHE_MISSES_CHROME": {
+    "kind": "exponential",
+    "high": "256",
+    "n_buckets": 30,
+    "description": "Word cache misses, chrome text (chars)"
   },
   "FONT_CACHE_HIT": {
     "kind": "boolean",