Add UMA stats for pen palette

ash/common/system/chromeos/palette/common_palette_tool.cc

Index: ash/common/system/chromeos/palette/common_palette_tool.cc
diff --git a/ash/common/system/chromeos/palette/common_palette_tool.cc b/ash/common/system/chromeos/palette/common_palette_tool.cc
index f71b87cd06e312493653ebc0cb8434476e4f0a53..344f453806536b64b8b0b1adca90a4a639e2d381 100644
--- a/ash/common/system/chromeos/palette/common_palette_tool.cc
+++ b/ash/common/system/chromeos/palette/common_palette_tool.cc
@@ -10,6 +10,7 @@
 #include "ash/common/system/tray/hover_highlight_view.h"
 #include "ash/common/system/tray/view_click_listener.h"
 #include "base/logging.h"
+#include "base/metrics/histogram_macros.h"
 #include "base/strings/utf_string_conversions.h"
 #include "grit/ash_resources.h"
 #include "ui/base/resource/resource_bundle.h"
@@ -51,6 +52,7 @@ void CommonPaletteTool::OnViewDestroyed() {
 
 void CommonPaletteTool::OnEnable() {
   PaletteTool::OnEnable();
+  start_time_ = base::TimeTicks::Now();
 
   if (highlight_view_) {
     highlight_view_->SetHighlight(true);
@@ -61,6 +63,14 @@ void CommonPaletteTool::OnEnable() {
 void CommonPaletteTool::OnDisable() {
   PaletteTool::OnDisable();
 
+  if (GetToolId() == ash::PaletteToolId::LASER_POINTER) {

[jdufault, 2016/09/02 21:54:30]

What about something like

if (ShouldRecordUma(GetToolId())
  UMA_HISTOGRAM...(GetUmaName(GetToolId()), ...);

And then ShouldRecordUma / GetUmaName are defined in the anonymous namespace of
this file.

Though to avoid pulling in every tool type for this specific file maybe we want
to do something like

if (GetActiveDurationUmaName())
  UMA_HISTOGRAM(GetActiveDurationUmaName(), ...)

Where GetActiveDurationUmaName() is a virtual method that returns an std::string
instance. If the tool wants to record an UMA value, it returns a non-empty
string.

[Ilya Sherman, 2016/09/02 22:02:49]

Histogram names passed to UMA_HISTOGRAM_ macros must be runtime constant, so I
don't think your suggestion will work.  You'll either need to call the
underlying C++ code directly, or have different code paths for different
histogram names.

+    UMA_HISTOGRAM_LONG_TIMES_100("Ash.Shelf.Palette.InLaserPointerMode",

[Ilya Sherman, 2016/09/02 21:39:30]

Hmm, are values under 100 ms at all likely?  I would recommend using an
UMA_HISTOGRAM_CUSTOM_TIMES, with 50 buckets, and a higher minimum.  Ditto below.

[xiaoyinh(OOO Sep 11-29), 2016/09/06 17:40:04]

Done.

+                                 base::TimeTicks::Now() - start_time_);
+  } else if (GetToolId() == ash::PaletteToolId::MAGNIFY) {
+    UMA_HISTOGRAM_LONG_TIMES_100("Ash.Shelf.Palette.InMagnifyMode",
+                                 base::TimeTicks::Now() - start_time_);
+  }
+
   if (highlight_view_) {
     highlight_view_->SetHighlight(false);
     highlight_view_->SetRightIconVisible(false);
@@ -68,6 +78,8 @@ void CommonPaletteTool::OnDisable() {
 }
 
 void CommonPaletteTool::OnViewClicked(views::View* sender) {
+  delegate()->RecordPaletteMetrics(
+      PaletteToolIdToPaletteTrayOptions(GetToolId()));
   if (enabled())
     delegate()->DisableTool(GetToolId());
   else