Disable timing from chrome://profiler on Android.

base/profiler/tracked_time.cc

Index: base/profiler/tracked_time.cc
diff --git a/base/profiler/tracked_time.cc b/base/profiler/tracked_time.cc
index 7791c3adc6b8580f09ccffd100bc6a2dd241c81f..6de9945cc21eecd29b592911e5d24d8db07ba7fa 100644
--- a/base/profiler/tracked_time.cc
+++ b/base/profiler/tracked_time.cc
@@ -4,12 +4,29 @@
 
 #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) {}
@@ -51,6 +68,8 @@ TrackedTime::TrackedTime(const base::TimeTicks& time)
 
 // 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"