Collect UMA statistics on which chrome://flags lead to chrome restart on ChromeOS.

chrome/browser/about_flags.cc

Index: chrome/browser/about_flags.cc
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index 7577556a0b3e3a97ca013d70cf3a88c938e8c25c..6c79d78b2a6ad493eedc81949896f517f312e5eb 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -11,6 +11,7 @@
 
 #include "base/command_line.h"
 #include "base/memory/singleton.h"
+#include "base/metrics/sparse_histogram.h"
 #include "base/stl_util.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/utf_string_conversions.h"
@@ -29,6 +30,7 @@
 #include "grit/generated_resources.h"
 #include "grit/google_chrome_strings.h"
 #include "media/base/media_switches.h"
+#include "third_party/zlib/zlib.h"
 #include "ui/base/l10n/l10n_util.h"
 #include "ui/base/ui_base_switches.h"
 #include "ui/display/display_switches.h"
@@ -61,6 +63,8 @@ using base::UserMetricsAction;
 
 namespace about_flags {
 
+const uint32_t kBadSwitchFormatHistogramId = 0;
+
 // Macros to simplify specifying the type.
 #define SINGLE_VALUE_TYPE_AND_VALUE(command_line_switch, switch_value) \
     Experiment::SINGLE_VALUE, \
@@ -1516,16 +1520,6 @@ const Experiment kExperiments[] = {
     kOsAndroid,
     SINGLE_VALUE_TYPE(switches::kEnableAccessibilityTabSwitcher)
   },
-  {
-    // TODO(dmazzoni): remove this flag when native android accessibility
-    // ships in the stable channel. http://crbug.com/356775
-    "enable-accessibility-script-injection",
-    IDS_FLAGS_ENABLE_ACCESSIBILITY_SCRIPT_INJECTION_NAME,
-    IDS_FLAGS_ENABLE_ACCESSIBILITY_SCRIPT_INJECTION_DESCRIPTION,
-    kOsAndroid,
-    // Java-only switch: ContentSwitches.ENABLE_ACCESSIBILITY_SCRIPT_INJECTION.
-    SINGLE_VALUE_TYPE("enable-accessibility-script-injection")
-  },

[Ilya Sherman, 2014/08/05 20:14:46]

This diff seems unrelated to your CL.

[Alexander Alekseev, 2014/08/07 23:24:55]

As this CL doesn't have explicit UMA IDs, this part looks irrelevant.
But at the beginning we agreed that I would drop this (unused) part,
and it saves extra ID from UMA.

Do you think we should reserve ID for this switch?

[Ilya Sherman, 2014/08/08 03:49:45]

If this switch is obsolete, I'd prefer that you remove it in a separate, tiny
CL, since it's easy for the change to get lost in a large CL like this one.

[Alexander Alekseev, 2014/08/09 01:30:00]

Done.

 #endif
   {
     "enable-one-copy",
@@ -1954,6 +1948,7 @@ class FlagsState {
       std::map<std::string, CommandLine::StringType>* switch_list);
   void ResetAllFlags(FlagsStorage* flags_storage);
   void reset();
+  std::set<std::string> GetAllSwitchesForTesting() const;
 
   // Returns the singleton instance of this class
   static FlagsState* GetInstance() {
@@ -2144,17 +2139,31 @@ void ConvertFlagsToSwitches(FlagsStorage* flags_storage,
 }
 
 bool AreSwitchesIdenticalToCurrentCommandLine(
-    const CommandLine& new_cmdline, const CommandLine& active_cmdline) {
+    const CommandLine& new_cmdline,
+    const CommandLine& active_cmdline,
+    std::set<CommandLine::StringType>* out_difference) {
   std::set<CommandLine::StringType> new_flags =
       ExtractFlagsFromCommandLine(new_cmdline);
   std::set<CommandLine::StringType> active_flags =
       ExtractFlagsFromCommandLine(active_cmdline);
 
+  bool result = false;
   // Needed because std::equal doesn't check if the 2nd set is empty.
-  if (new_flags.size() != active_flags.size())
-    return false;
+  if (new_flags.size() == active_flags.size()) {
+    result =
+        std::equal(new_flags.begin(), new_flags.end(), active_flags.begin());
+  }
 
-  return std::equal(new_flags.begin(), new_flags.end(), active_flags.begin());
+  if (out_difference && !result) {
+    std::set_symmetric_difference(
+        new_flags.begin(),
+        new_flags.end(),
+        active_flags.begin(),
+        active_flags.end(),
+        std::inserter(*out_difference, out_difference->begin()));
+  }
+
+  return result;
 }
 
 void GetFlagsExperimentsData(FlagsStorage* flags_storage,
@@ -2262,6 +2271,47 @@ void RecordUMAStatistics(FlagsStorage* flags_storage) {
   content::RecordAction(UserMetricsAction("StartupTick"));
 }
 
+uint32 GetSwitchUMAId(const std::string& switch_name) {
+  return static_cast<unsigned>(

[Ilya Sherman, 2014/08/05 20:14:46]

Please cast directly to the returned type, i.e. uint32.  Also, please use a
checked_cast.

[Alexander Alekseev, 2014/08/07 23:24:56]

Done.

+      crc32(0,

[Ilya Sherman, 2014/08/05 20:14:46]

Optional: md5 is more commonly used for UMA code.  It's fine to use any hash
function you like here, but you might want to at least double-check whether
Dremel natively supports crc32 before using it.

[Alexander Alekseev, 2014/08/07 23:24:56]

On a server-side it looks like uint32, so it doesn't need special suport, does
it?

Also, MD5 doesn't fit 32bit integer, so what ID type should I use here?

[Ilya Sherman, 2014/08/08 03:49:45]

The only reason that special support might be useful is that it's convenient for
users to be able to type something like CRC("--enable-my-feature") in Dremel,
without having to compute the CRC themselves.
For other UMA code, we just trim the MD5 hash as needed.

+            reinterpret_cast<const Bytef*>(switch_name.c_str()),
+            switch_name.length()));
+}
+
+void ReportCustomFlags(const std::string& uma_histogram_hame,
+                       const std::set<std::string>& command_line_difference) {
+  for (std::set<std::string>::const_iterator it =
+           command_line_difference.begin();
+       it != command_line_difference.end();
+       ++it) {
+    int uma_id = about_flags::kBadSwitchFormatHistogramId;
+    if (it->size() > 2) {

[Ilya Sherman, 2014/08/05 20:14:46]

It seems more appropriate to check the actual characters of the prefix, rather
than just its length.

[Alexander Alekseev, 2014/08/07 23:24:56]

Done.

+      // Skip '--' before switch name.
+      std::string switch_name(it->substr(2));
+
+      // Kill value, if any.
+      const size_t value_pos = switch_name.find('=');
+      if (value_pos != std::string::npos)
+        switch_name.resize(value_pos);
+
+      uma_id = GetSwitchUMAId(switch_name);
+    } else {
+      NOTREACHED() << "ReportCustomFlags(): flag '" << *it
+                   << "' has incorrect format.";
+    }
+    VLOG(1) << "ReportCustomFlags(): histogram='" << uma_histogram_hame << "' '"
+            << *it << "', uma_id=" << uma_id;
+
+    // Sparse histogram macro does not cache the histogram, so it's safe
+    // to use macro with non-static histogram name here.
+    UMA_HISTOGRAM_SPARSE_SLOWLY(uma_histogram_hame, uma_id);
+  }
+}
+
+std::set<std::string> GetAllSwitchesForTesting() {
+  return FlagsState::GetInstance()->GetAllSwitchesForTesting();
+}
+
 //////////////////////////////////////////////////////////////////////////////
 // FlagsState implementation.
 
@@ -2431,6 +2481,26 @@ void FlagsState::reset() {
   flags_switches_.clear();
 }
 
+std::set<std::string> FlagsState::GetAllSwitchesForTesting() const {
+  std::set<std::string> result;
+
+  for (size_t i = 0; i < num_experiments; ++i) {
+    const Experiment& e = experiments[i];

[Ilya Sherman, 2014/08/05 20:14:46]

nit: Please use complete variable names rather than abbreviations.

[Alexander Alekseev, 2014/08/07 23:24:56]

Done.

+    if (e.type == Experiment::SINGLE_VALUE) {
+      result.insert(e.command_line_switch);
+    } else if (e.type == Experiment::MULTI_VALUE) {
+      for (int j = 0; j < e.num_choices; ++j) {
+        result.insert(e.choices[j].command_line_switch);
+      }
+    } else {
+      DCHECK_EQ(e.type, Experiment::ENABLE_DISABLE_VALUE);
+      result.insert(e.command_line_switch);
+      result.insert(e.disable_command_line_switch);
+    }
+  }
+  return result;
+}

[Ilya Sherman, 2014/08/05 20:14:46]

Why isn't this in the testing namespace below?  In fact, it looks like you could
just use GetExperiments() from below, and then implement this function in the
test file.

[Alexander Alekseev, 2014/08/07 23:24:56]

Done.

+
 }  // namespace
 
 namespace testing {