Stack sampling profiler: enable at 10% for GPU process on canary

chrome/common/stack_sampling_configuration.h

Index: chrome/common/stack_sampling_configuration.h
diff --git a/chrome/common/stack_sampling_configuration.h b/chrome/common/stack_sampling_configuration.h
index 1400d741590863a1f036beff661c890c14b2c598..452c4eee9e62c0987d62c74dccabc1793135f31f 100644
--- a/chrome/common/stack_sampling_configuration.h
+++ b/chrome/common/stack_sampling_configuration.h
@@ -32,7 +32,8 @@ class StackSamplingConfiguration {
 
   // Get the synthetic field trial configuration. Returns true if a synthetic
   // field trial should be registered. This should only be called from the
-  // browser process.
+  // browser process. When run at startup, the profiler must use a synthetic
+  // field trial since it runs before the metrics field trials are initialized.
   bool GetSyntheticFieldTrial(std::string* trial_name,
                               std::string* group_name) const;
 
@@ -46,6 +47,7 @@ class StackSamplingConfiguration {
   static StackSamplingConfiguration* Get();
 
  private:
+  // Configuration to use for this Chrome instance.
   enum ProfileConfiguration {
     // Chrome-wide configurations set in the browser process.
     PROFILE_DISABLED,
@@ -59,6 +61,18 @@ class StackSamplingConfiguration {
     PROFILE_FROM_COMMAND_LINE
   };
 
+  // Configuration variations, along with weights to use when randomly choosing
+  // one of a set of variations.
+  struct Variation {
+    ProfileConfiguration config;
+    int weight;
+  };
+
+  // Randomly chooses a configuration from the weighted variations. Weights are
+  // expected to sum to 100 as a sanity check.
+  static ProfileConfiguration ChooseConfiguration(
+      const std::vector<Variation>& variations);
+
   // Generates sampling profiler configurations for all processes.
   static ProfileConfiguration GenerateConfiguration();