Histogram definition for Accelerated Fixed Root Background measurements.

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 2d1fec4ab8bb3127aba66a58dbacafabacfcdf14..0e2a0dd6bd7977356b482afefa9d8223fc91cb0f 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -12753,6 +12753,15 @@ other types of suffix sets.
   </summary>
 </histogram>
 
+<histogram name="Renderer.AcceleratedFixedRootBackground"
+    enum="AcceleratedFixedRootBackground">
+  <summary>
+    Keeps track of the number of main frame scrolls with an accelerated fixed
+    root background, the number of main frame scrolls with an unaccelerated
+    fixed root background, and the total number of main frame scrolls.
+  </summary>
+</histogram>
+
 <histogram name="Renderer.CompositedScrolling" enum="CompositedScrolling">
   <summary>
     Total count of the number of RenderLayers which are scrollable areas, need
@@ -18103,6 +18112,12 @@ other types of suffix sets.
   <int value="1" label="Abandoned"/>
 </enum>
 
+<enum name="AcceleratedFixedRootBackground" type="int">
+  <int value="0" label="ScrolledMainFrame"/>
+  <int value="1" label="ScrolledMainFrameWithAcceleratedFixedRootBackground"/>
+  <int value="2" label="ScrolledMainFrameWithUnacceleratedFixedRootBackground"/>
+</enum>
+
 <enum name="AndroidEvictionReason" type="int">
   <int value="0" label="TabUnusedTooLong"/>
   <int value="1" label="TabUnusedInSession"/>