Disable timing from chrome://profiler on Android.

base/profiler/tracked_time.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/profiler/tracked_time.h"
 
+#include "base/base_switches.h"
+#include "base/command_line.h"
 #include "build/build_config.h"
 
 #if defined(OS_WIN)
 #include <mmsystem.h>  // Declare timeGetTime()... after including build_config.
 #endif
 
+namespace {
+inline bool IsProfilerTimingDisabled() {

[jar (doing other things), 2013/12/02 19:01:50]

Nit: code is IMO always much more confusing when negatives are used in flags and
function.  I try to make it a habit to use positives as much as possible.

As a result, I'd much rather see the (very similar) function:
IsProfilerTimingEnabled().

[qsr, 2013/12/03 11:33:44]

 Done. But I didn't change the static variable, as I need the default value to
correspond to a negative value for it.

+  // This initialization is not thread safe. In particular, some early calls
+  // might see |timing_disabled| being false, even if this is incorrect. This is
+  // OK, as the timing is only disabled for performance reasons, and having a
+  // few calls to TimeTicks::Now() is acceptable, while needing to use a lock or
+  // a memory barrier would be more costly.
+  static bool timing_disabled = CommandLine::ForCurrentProcess()->HasSwitch(
+                                    switches::kDisableProfilerTiming) &&
+                                !CommandLine::ForCurrentProcess()->HasSwitch(
+                                     switches::kEnableProfilerTiming);
+  return timing_disabled;
+}
+}  // namespace
+
 namespace tracked_objects {
 
 Duration::Duration() : ms_(0) {}
 Duration::Duration(int32 duration) : ms_(duration) {}
 
 Duration& Duration::operator+=(const Duration& other) {
   ms_ += other.ms_;
   return *this;
 }
 
@@ skipping 21 matching lines @@
 //------------------------------------------------------------------------------
 
 TrackedTime::TrackedTime() : ms_(0) {}
 TrackedTime::TrackedTime(int32 ms) : ms_(ms) {}
 TrackedTime::TrackedTime(const base::TimeTicks& time)
     : ms_((time - base::TimeTicks()).InMilliseconds()) {
 }
 
 // static
 TrackedTime TrackedTime::Now() {
+  if (IsProfilerTimingDisabled())
+    return TrackedTime();
 #if defined(OS_WIN)
   // Use lock-free accessor to 32 bit time.
   // Note that TimeTicks::Now() is built on this, so we have "compatible"
   // times when we down-convert a TimeTicks sample.
   return TrackedTime(base::TimeTicks::UnprotectedNow());
 #else
   // Posix has nice cheap 64 bit times, so we just down-convert it.
   return TrackedTime(base::TimeTicks::Now());
 #endif  // OS_WIN
 }
 
 Duration TrackedTime::operator-(const TrackedTime& other) const {
   return Duration(ms_ - other.ms_);
 }
 
 TrackedTime TrackedTime::operator+(const Duration& other) const {
   return TrackedTime(ms_ + other.ms_);
 }
 
 bool TrackedTime::is_null() const { return ms_ == 0; }
 
 }  // namespace tracked_objects