Introduce mojo interface for collecting StackSamplingProfiler data

base/profiler/stack_sampling_profiler.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_PROFILER_STACK_SAMPLING_PROFILER_H_
 #define BASE_PROFILER_STACK_SAMPLING_PROFILER_H_
 
 #include <stddef.h>
 
 #include <memory>
@@ skipping 229 matching lines @@
   PlatformThreadHandle sampling_thread_handle_;
 
   const CompletedCallback completed_callback_;
 
   // Stored until it can be passed to the NativeStackSampler created in Start().
   NativeStackSamplerTestDelegate* const test_delegate_;
 
   DISALLOW_COPY_AND_ASSIGN(StackSamplingProfiler);
 };
 
-// The metrics provider code wants to put Samples in a map and compare them,
-// which requires us to define a few operators.
+// These operators permit types to be compared and used in a map of Samples, as
+// done in tests and by the metrics provider code.
+BASE_EXPORT bool operator==(const StackSamplingProfiler::Module& a,
+                            const StackSamplingProfiler::Module& b);
 BASE_EXPORT bool operator==(const StackSamplingProfiler::Frame& a,
                             const StackSamplingProfiler::Frame& b);
 BASE_EXPORT bool operator<(const StackSamplingProfiler::Frame& a,
                            const StackSamplingProfiler::Frame& b);
 
 }  // namespace base
 
 #endif  // BASE_PROFILER_STACK_SAMPLING_PROFILER_H_