[Sampling profiler] Move to 50/50 experiment on Android canary

Move from a 10%/10% experiment to a 50%/50% experiment to provide the
maximum signal for analysis of experiment results. The implementation
in https://crrev.com/2453795 moves work to the render thread and this
enables evaluation of the impact in the wild.

Bug: 1004855
Change-Id: Id7c0c75bba2137aaccd78b7dd320fae0c7172004
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2458388Reviewed-by: Etienne Pierre-Doray <etiennep@chromium.org>
Commit-Queue: Mike Wittman <wittman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#814875}

chrome/common/profiler/thread_profiler_platform_configuration.cc

@@ -127,6 +127,9 @@ class AndroidPlatformConfiguration : public DefaultPlatformConfiguration {
   RuntimeModuleState GetRuntimeModuleState(
       base::Optional<version_info::Channel> release_channel) const override;
 
+  RelativePopulations GetEnableRates(
+      base::Optional<version_info::Channel> release_channel) const override;
+
   void RequestRuntimeModuleInstall() const override;
 
   double GetChildProcessEnableFraction(
@@ -175,6 +178,19 @@ AndroidPlatformConfiguration::GetRuntimeModuleState(
   return RuntimeModuleState::kModuleNotAvailable;
 }
 
+ThreadProfilerPlatformConfiguration::RelativePopulations
+AndroidPlatformConfiguration::GetEnableRates(
+    base::Optional<version_info::Channel> release_channel) const {
+  if (release_channel) {
+    CHECK(*release_channel == version_info::Channel::CANARY ||
+          *release_channel == version_info::Channel::DEV);
+    // Use a 50/50 experiment to maximize signal in the relevant metrics.
+    return RelativePopulations{0, 50};
+  }
+
+  return DefaultPlatformConfiguration::GetEnableRates(release_channel);
+}
+
 void AndroidPlatformConfiguration::RequestRuntimeModuleInstall() const {
   // The install can only be done in the browser process.
   CHECK_EQ(metrics::CallStackProfileParams::BROWSER_PROCESS,

chrome/common/profiler/thread_profiler_platform_configuration_unittest.cc

@@ -128,13 +128,15 @@ MAYBE_PLATFORM_CONFIG_TEST_F(ThreadProfilerPlatformConfigurationTest,
                              GetEnableRates) {
   using RelativePopulations =
       ThreadProfilerPlatformConfiguration::RelativePopulations;
-  EXPECT_EQ((RelativePopulations{80, 20}),
-            config()->GetEnableRates(version_info::Channel::CANARY));
 #if defined(OS_ANDROID)
+  EXPECT_EQ((RelativePopulations{0, 50}),
+            config()->GetEnableRates(version_info::Channel::CANARY));
   // Note: death tests aren't supported on Android. Otherwise this test would
   // check that the other inputs result in CHECKs.
 #else
   EXPECT_CHECK_DEATH(config()->GetEnableRates(version_info::Channel::UNKNOWN));
+  EXPECT_EQ((RelativePopulations{80, 20}),
+            config()->GetEnableRates(version_info::Channel::CANARY));
   EXPECT_EQ((RelativePopulations{80, 20}),
             config()->GetEnableRates(version_info::Channel::DEV));
   EXPECT_CHECK_DEATH(config()->GetEnableRates(version_info::Channel::BETA));