Add UMAs for gpu rasterization .

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 96b852964ae67fbca51d8a9efdb302a212c08333..8b711f4d17e79377349939aa97212fab86e47183 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -22214,6 +22214,40 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="Renderer4.GpuRasterizationEnabled" units="BooleanEnabled">
+  <owner>alokp@chromium.org</owner>
+  <summary>
+    Whether gpu rasterization is enabled (checked once after the page is painted
+    for the first time).
+  </summary>
+</histogram>
+
+<histogram name="Renderer4.GpuRasterizationSuitableContent"
+    units="BooleanEnabled">
+  <owner>alokp@chromium.org</owner>
+  <summary>
+    If gpu rasterization is enabled, whether the page contents are suitable for
+    gpu rasterization (checked once after the page is painted for the first
+    time).
+  </summary>
+</histogram>
+
+<histogram name="Renderer4.GpuRasterizationTriggered" units="BooleanEnabled">
+  <owner>alokp@chromium.org</owner>
+  <summary>
+    If gpu rasterization is enabled, whether it was triggered (checked once
+    after the page is painted for the first time).
+  </summary>
+</histogram>
+
+<histogram name="Renderer4.GpuRasterizationUsed" units="BooleanEnabled">
+  <owner>alokp@chromium.org</owner>
+  <summary>
+    If gpu rasterization is enabled, whether it was actually used for the page
+    (checked once after the page is painted for the first time).
+  </summary>
+</histogram>
+
 <histogram name="Renderer4.InvalidationRegionApproximateRectCount"
     units="rects">
   <owner>wiltzius@chromium.org</owner>