Use low entropy for studies that send experiment IDs to Google properties.

This applies to all clients, even those that have metrics reporting enabled. This will cause a reshuffle of any study that is sending experiment IDs.

BUG=612666

Review-Url: https://codereview.chromium.org/1984003002
Cr-Commit-Position: refs/heads/master@{#394544}
diff --git a/base/test/mock_entropy_provider.cc b/base/test/mock_entropy_provider.cc
index a4cc972..5ebf19a 100644
--- a/base/test/mock_entropy_provider.cc
+++ b/base/test/mock_entropy_provider.cc
@@ -6,12 +6,15 @@
 
 namespace base {
 
+MockEntropyProvider::MockEntropyProvider() : entropy_value_(0.5) {}
+MockEntropyProvider::MockEntropyProvider(double entropy_value)
+    : entropy_value_(entropy_value) {}
 MockEntropyProvider::~MockEntropyProvider() {}
 
 double MockEntropyProvider::GetEntropyForTrial(
     const std::string& trial_name,
     uint32_t randomization_seed) const {
-  return 0.5;
+  return entropy_value_;
 }
 
 }  // namespace base