Disable timing from chrome://profiler on Android.

On Android, on a arm CPU, TimeTicks::Now() is taking 900ns (20 times
what it takes on a desktop x86 CPU). The bigger user of TimeTicks::Now()
is tracked_objects::TrackedTime, and this impacts the overall
performance of Chrome on this platform.

This CL adds compile line flags that allows to disable
tracked_objects::TrackedTime. It also disable
tracked_objects::TrackedTime by default on Android.

BUG=315070

Review URL: https://codereview.chromium.org/99343002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@240092 0039d316-1c4b-4281-b951-d872f2087c98

base/base_switches.cc

@@ -54,6 +54,14 @@ const char kWaitForDebugger[]               = "wait-for-debugger";
 // Sends a pretty-printed version of tracing info to the console.
 const char kTraceToConsole[]                = "trace-to-console";
 
+// Configure whether chrome://profiler will contain timing information. This
+// option is enabled by default. A value of "0" will disable profiler timing,
+// while all other values will enable it.
+const char kProfilerTiming[]                = "profiler-timing";
+// Value of the --profiler-timing flag that will disable timing information for
+// chrome://profiler.
+const char kProfilerTimingDisabledValue[]   = "0";
+
 #if defined(OS_POSIX)
 // Used for turning on Breakpad crash reporting in a debug environment where
 // crash reporting is typically compiled but disabled.

base/base_switches.h

@@ -17,11 +17,13 @@ extern const char kEnableCrashReporter[];
 extern const char kEnableDCHECK[];
 extern const char kFullMemoryCrashReport[];
 extern const char kNoErrorDialogs[];
+extern const char kProfilerTiming[];
+extern const char kProfilerTimingDisabledValue[];
 extern const char kTestChildProcess[];
+extern const char kTraceToConsole[];
 extern const char kV[];
 extern const char kVModule[];
 extern const char kWaitForDebugger[];
-extern const char kTraceToConsole[];
 
 #if defined(OS_POSIX)
 extern const char kEnableCrashReporterForTesting[];

base/tracked_objects.cc

@@ -7,6 +7,8 @@
 #include <limits.h>
 #include <stdlib.h>
 
+#include "base/base_switches.h"
+#include "base/command_line.h"
 #include "base/compiler_specific.h"
 #include "base/debug/leak_annotations.h"
 #include "base/logging.h"
@@ -51,6 +53,28 @@ const ThreadData::Status kInitialStartupState =
 // problem with its presence).
 static const bool kAllowAlternateTimeSourceHandling = true;
 
+inline bool IsProfilerTimingEnabled() {
+  static enum {
+    UNDEFINED_TIMING,
+    ENABLED_TIMING,
+    DISABLED_TIMING,
+  } timing_enabled = UNDEFINED_TIMING;
+  // This initialization is not thread-safe, so the value of |timing_enabled|
+  // can be computed multiple times. This is not an issue, as the computed value
+  // will always be the same, and is side-effect free, while needing to use a
+  // lock or a memory barrier would be more costly.
+  if (timing_enabled == UNDEFINED_TIMING) {
+    if (!CommandLine::InitializedForCurrentProcess())
+      return true;
+    timing_enabled = (CommandLine::ForCurrentProcess()->GetSwitchValueASCII(
+                          switches::kProfilerTiming) ==
+                      switches::kProfilerTimingDisabledValue)
+                         ? DISABLED_TIMING
+                         : ENABLED_TIMING;
+  }
+  return timing_enabled == ENABLED_TIMING;
+}
+
 }  // namespace
 
 //------------------------------------------------------------------------------
@@ -754,7 +778,7 @@ void ThreadData::SetAlternateTimeSource(NowFunction* now_function) {
 TrackedTime ThreadData::Now() {
   if (kAllowAlternateTimeSourceHandling && now_function_)
     return TrackedTime::FromMilliseconds((*now_function_)());
-  if (kTrackAllTaskObjects && TrackingStatus())
+  if (kTrackAllTaskObjects && IsProfilerTimingEnabled() && TrackingStatus())
     return TrackedTime::Now();
   return TrackedTime();  // Super fast when disabled, or not compiled.
 }

content/browser/android/content_startup_flags.cc

@@ -4,6 +4,7 @@
 
 #include "content/browser/android/content_startup_flags.h"
 
+#include "base/base_switches.h"
 #include "base/command_line.h"
 #include "base/logging.h"
 #include "base/strings/string_number_conversions.h"
@@ -89,6 +90,12 @@ void SetContentCommandLineFlags(int max_render_process_count,
     parsed_command_line->AppendSwitchNative(
       switches::kRegisterPepperPlugins, plugin_descriptor);
   }
+
+  // Disable profiler timing by default.
+  if (!parsed_command_line->HasSwitch(switches::kProfilerTiming)) {
+    parsed_command_line->AppendSwitchASCII(
+        switches::kProfilerTiming, switches::kProfilerTimingDisabledValue);
+  }
 }
 
 }  // namespace content

content/browser/renderer_host/render_process_host_impl.cc

@@ -1037,6 +1037,7 @@ void RenderProcessHostImpl::PropagateBrowserCommandLineToRenderer(
     switches::kNoReferrers,
     switches::kNoSandbox,
     switches::kPpapiInProcess,
+    switches::kProfilerTiming,
     switches::kRegisterPepperPlugins,
     switches::kRendererAssertTest,
     switches::kRendererStartupDialog,