Implement fallback cache

tools/metrics/histograms/histograms.xml

Index: tools/metrics/histograms/histograms.xml
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index e91215e18b9c350f62cdea0c5997469dcb8355d0..17502fdbdc1fb8e46f366a7ae198b6a15154e4d5 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -8394,6 +8394,21 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="DirectWrite.Fonts.Proxy.Fallback.CacheSize" units="Count">
+  <owner>kulshin@chromium.org</owner>
+  <summary>Records how many font families are in the fallback cache.</summary>
+</histogram>
+
+<histogram name="DirectWrite.Fonts.Proxy.FallbackResult"
+    enum="DirectWriteFontFallbackResult">
+  <owner>kulshin@chromium.org</owner>
+  <summary>
+    Measures the effectiveness of the font fallback proxy. This tracks if we
+    were able to find a suitable font to render the character, and whether an
+    IPC was necessary.
+  </summary>
+</histogram>
+
 <histogram name="DirectWrite.Fonts.Proxy.LoaderType"
     enum="DirectWriteFontLoaderType">
   <owner>kulshin@chromium.org</owner>
@@ -65550,6 +65565,12 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <int value="1" label="Failed"/>
 </enum>
 
+<enum name="DirectWriteFontFallbackResult" type="int">
+  <int value="0" label="Failed: no font matched"/>
+  <int value="1" label="Success: mapped from cache"/>
+  <int value="2" label="Success: mapped using IPC"/>
+</enum>
+
 <enum name="DirectWriteFontLoaderType" type="int">
   <int value="0" label="File: system font directory"/>
   <int value="1" label="File: outside sandbox whitelist"/>