Add histograms for MouseEventPrefetch.Mouse*

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 535d3bcc75c299c05a279f2200f158f49038f860..144d04199bf33a2dcc0d454a5f3f283708efadaf 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -1084,6 +1084,50 @@ other types of suffix sets.
   </summary>
 </histogram>
 
+<histogram name="MouseEventPrefetch.MouseDownDuration_Click" units="ms">
+  <summary>
+    Measures the time elapsed between when the user mousedown-ed a link and when
+    the user clicked a link.
+  </summary>
+</histogram>
+
+<histogram name="MouseEventPrefetch.MouseDownFollowedByClick"
+    enum="MouseEventFollowedByClick">
+  <summary>
+    Caught: The number of mousedown events detected prior to HTML anchor-tag
+    links' default click event handler. Miss: The number of HTML anchor-tag
+    links' default click events without prior mousedown events.

[Ilya Sherman, 2013/05/07 08:52:23]

Optional nit: I think this description would be easier to understand if it were
worded something more like:

"For each click handled by an HTML anchor tag link, whether Blink [or some other
system?] saw a mousedown event preceding it.  This is only measured for clicks
handled by the anchor tag's default click event handler."

+  </summary>
+</histogram>
+
+<histogram name="MouseEventPrefetch.MouseDowns">
+  <summary>
+    The number of mousedown events detected at HTML anchor-tag links' default
+    event handler.
+  </summary>
+</histogram>
+
+<histogram name="MouseEventPrefetch.MouseOverDuration_Click" units="ms">
+  <summary>
+    Measures the time elapsed between when the user mouseover-ed a link and when
+    the user clicked a link.
+  </summary>
+</histogram>
+
+<histogram name="MouseEventPrefetch.MouseOverDuration_NoClick" units="ms">
+  <summary>
+    Measures the time elapsed between when the user mouseover-ed a link and when
+    the user mouseout-ed a link without click.
+  </summary>
+</histogram>
+
+<histogram name="MouseEventPrefetch.MouseOvers">
+  <summary>
+    The number of mouseover events detected at HTML anchor-tag links' default
+    event handler.
+  </summary>
+</histogram>
+
 <histogram name="Navigation.MainFrameScheme" enum="NavigationScheme">
   <summary>The scheme of the URL for each main-frame navigation.</summary>
 </histogram>
@@ -9357,6 +9401,11 @@ other types of suffix sets.
   <int value="9" label="PRERENDER_LOAD">Speculative prerendering of a page</int>
 </enum>
 
+<enum name="MouseEventFollowedByClick" type="int">
+  <int value="0" label="Caught_event_before_click"/>

[Ilya Sherman, 2013/05/07 08:52:23]

nit: No need for underscores; you can use spaces.  This is a human-readable
label.

+  <int value="1" label="Miss_event_before_click"/>

[Ilya Sherman, 2013/05/07 08:52:23]

Ditto.  Also, probably "Missed" rather than "Miss"

+</enum>
+
 <enum name="NavigationScheme" type="int">
   <int value="0" label="(Unknown)"/>
   <int value="1" label="http"/>