Metrics for unique users of key assistive technologies

Accessibility metrics are fired once, 45 seconds after startup.
However, UMA counts unique users on a daily basis.

This means that the metrics system is only counting 1/2 of users who don't
relaunch their browser in a 2 day period. Or 1/3 of users who don't
relaunch for 3 days, etc.

Adding the following *.EveryReport alternate histogram names for
histograms that fire more often. These can be used with the unique
users aggregation option when viewing metrics:
Accessibility.CrosSpokenFeedback.EveryReport
Accessibility.Android.ScreenReader.EveryReport,
Accessibility.Mac.ScreenReader.EveryReport,
Accessibility.WinScreenReader2.EveryReport,
Accessibility.WinJAWS.EveryReport
Accessibility.WinNVDA.EveryReport
Accessibility.WinZoomText.EveryReport

(cherry picked from commit 81ce2bd7582c2ea1e75969905d02dcaa636e36b1)

Bug: 988502
Change-Id: I0b29dc35615668aafb7e873e574c1ba7ae280ead
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1724698
Commit-Queue: Aaron Leventhal <[email protected]>
Reviewed-by: Jesse Doherty <[email protected]>
Reviewed-by: Nektarios Paisios <[email protected]>
Cr-Original-Commit-Position: refs/heads/master@{#682971}
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1746847
Reviewed-by: Aaron Leventhal <[email protected]>
Cr-Commit-Position: refs/branch-heads/3865@{#309}
Cr-Branched-From: 0cdcc6158160790658d1f033d3db873603250124-refs/heads/master@{#681094}
diff --git a/content/browser/accessibility/browser_accessibility_state_impl.cc b/content/browser/accessibility/browser_accessibility_state_impl.cc
index 6a8924b..73a7642 100644
--- a/content/browser/accessibility/browser_accessibility_state_impl.cc
+++ b/content/browser/accessibility/browser_accessibility_state_impl.cc
@@ -8,6 +8,7 @@
 
 #include "base/bind.h"
 #include "base/command_line.h"
+#include "base/metrics/histogram_functions.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/task/post_task.h"
 #include "build/build_config.h"
@@ -195,6 +196,7 @@
     UpdatePlatformSpecificHistogramsOnUIThread() {}
 void BrowserAccessibilityStateImpl::
     UpdatePlatformSpecificHistogramsOnOtherThread() {}
+void BrowserAccessibilityStateImpl::UpdateUniqueUserHistograms() {}
 #endif
 
 void BrowserAccessibilityStateImpl::AddAccessibilityModeFlags(ui::AXMode mode) {