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..d26d3286b39ea7583df170c36450a2b284a7386f 100644
--- a/chrome/common/stack_sampling_configuration.h
+++ b/chrome/common/stack_sampling_configuration.h
@@ -46,6 +46,7 @@ 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 +60,18 @@ 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 must
+  // sum to 100.

[Ilya Sherman, 2016/10/12 20:52:31]

Why are weights required to sum to 100?  What if you want to run a 33%/33%/33%
trial?  (This restriction isn't present in the //base variations code, which is
why I'm asking why it's needed here.)

[Mike Wittman, 2016/10/12 21:50:41]

It's not strictly needed, but is a small sanity check. If I need a configuration
that doesn't work with this in the future I'll remove the constraint and DCHECK
at that point.

[Ilya Sherman, 2016/10/12 22:16:17]

Got it, that makes sense.  Would be nice to briefly document somewhere that this
is done as a config sanity-check =)

[Mike Wittman, 2016/10/12 23:00:32]

Done.

+  static ProfileConfiguration ChooseConfiguration(
+      const std::vector<Variation>& variations);
+
   // Generates sampling profiler configurations for all processes.
   static ProfileConfiguration GenerateConfiguration();