Add Desktop iOS promotion logging to chrome ios app.

ios/chrome/browser/desktop_promotion/histogram_macros.h

Index: ios/chrome/browser/desktop_promotion/histogram_macros.h
diff --git a/ios/chrome/browser/desktop_promotion/histogram_macros.h b/ios/chrome/browser/desktop_promotion/histogram_macros.h
new file mode 100644
index 0000000000000000000000000000000000000000..289a9774d3a68f6e5f951e0192933c73ca0d485f
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+++ b/ios/chrome/browser/desktop_promotion/histogram_macros.h
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+// Copyright 2017 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 IOS_CHROME_BROWSER_DESKTOP_PROMOTION_HISTOGRAM_MACROS_H_
+#define IOS_CHROME_BROWSER_DESKTOP_PROMOTION_HISTOGRAM_MACROS_H_
+
+#include "base/metrics/histogram.h"
+
+// HISTOGRAM_POINTER_BLOCK differ from STATIC_HISTOGRAM_POINTER_BLOCK
+// on using static histogram pointer, in this one we create a new histogram
+// from the histogram_factory_get_invocation each time this is called.
+// This is needed on the desktop promotion logging as there are cases where the
+// same call will be trying to log different histogram names.
+#define HISTOGRAM_POINTER_BLOCK(constant_histogram_name,                       \
+                                histogram_add_method_invocation,               \
+                                histogram_factory_get_invocation)              \
+  do {                                                                         \
+    base::HistogramBase* histogram_pointer = histogram_factory_get_invocation; \
+    histogram_pointer->histogram_add_method_invocation;                        \
+  } while (0)
+
+// This UMA_HISTOGRAM_CUSTOM_COUNT_NO_CACHE uses the HISTOGRAM_POINTER_BLOCK
+// instead of STATIC_HISTOGRAM_POINTER_BLOCK which handles being called with
+// different names from same function.
+#define UMA_HISTOGRAM_CUSTOM_COUNT_NO_CACHE(name, sample, min, max, \
+                                            bucket_count)           \
+  HISTOGRAM_POINTER_BLOCK(name, Add(sample),                        \
+                          base::Histogram::FactoryGet(              \
+                              name, min, max, bucket_count,         \
+                              base::HistogramBase::kUmaTargetedHistogramFlag))
+
+// Count histogram with no caching. This is used for collecting numeric data
+// when the number of buckets is 50 and the max value doesn't exceed 1000.
+#define UMA_HISTOGRAM_COUNT_1000_NO_CACHE(name, sample) \
+  UMA_HISTOGRAM_CUSTOM_COUNT_NO_CACHE(name, sample, 1, 1000, 50)
+
+#endif  // IOS_CHROME_BROWSER_DESKTOP_PROMOTION_HISTOGRAM_MACROS_H_