Add histogram for cancel button in blocked mixed content infobars.

chrome/browser/tab_contents/blocked_infobar_delegate.cc

Index: chrome/browser/tab_contents/blocked_infobar_delegate.cc
===================================================================
--- chrome/browser/tab_contents/blocked_infobar_delegate.cc	(revision 89528)
+++ chrome/browser/tab_contents/blocked_infobar_delegate.cc	(working copy)
@@ -103,6 +103,14 @@
   return true;
 }
 
+bool BlockedDisplayingInfoBarDelegate::Cancel() {
+  UMA_HISTOGRAM_ENUMERATION("MixedContent.DisplayingInfoBar",
+                            BLOCKED_INFOBAR_EVENT_CANCELLED,
+                            BLOCKED_INFOBAR_EVENT_LAST);
+  return true;
+}
+
+
 BlockedRunningInfoBarDelegate::BlockedRunningInfoBarDelegate(
     TabContentsWrapper* wrapper)
     : BlockedInfoBarDelegate(
@@ -136,3 +144,10 @@
   return true;
 }
 
+bool BlockedRunningInfoBarDelegate::Cancel() {
+  UMA_HISTOGRAM_ENUMERATION("MixedContent.RunningInfoBar",
+                            BLOCKED_INFOBAR_EVENT_CANCELLED,
+                            BLOCKED_INFOBAR_EVENT_LAST);
+  return true;
+}
+