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

base/test/mock_entropy_provider.h

Index: base/test/mock_entropy_provider.h
diff --git a/base/test/mock_entropy_provider.h b/base/test/mock_entropy_provider.h
index 32e9332e109ebf788c80a3685303e3633487a366..ca2b4bc8fe05d39b760c9c1a2b69d5373548d3da 100644
--- a/base/test/mock_entropy_provider.h
+++ b/base/test/mock_entropy_provider.h
@@ -13,11 +13,18 @@ namespace base {
 
 class MockEntropyProvider : public base::FieldTrial::EntropyProvider {
  public:
+  MockEntropyProvider();
+  explicit MockEntropyProvider(double entropy_value);
   ~MockEntropyProvider() override;
 
   // base::FieldTrial::EntropyProvider:
   double GetEntropyForTrial(const std::string& trial_name,
                             uint32_t randomization_seed) const override;
+
+ private:
+  double entropy_value_;
+
+  DISALLOW_COPY_AND_ASSIGN(MockEntropyProvider);
 };
 
 }  // namespace base