[StyleGuide] Allow begin and end non-member functions

Allow usage of |std::begin| and |std::end|. This is useful for iterating
fixed-size arrays.

Discussion thread: https://groups.google.com/a/chromium.org/d/topic/cxx/5iFNE8P5qT4/discussion

Furthermore, this CL replaces home-brewn |std::end|-like functions in
base/trace_event with |std::end| to verify that <iterator> is supported
on all platforms.

Review URL: https://codereview.chromium.org/1471683002

Cr-Commit-Position: refs/heads/master@{#361192}

base/trace_event/heap_profiler_allocation_context_tracker.cc

@@ -5,6 +5,7 @@
 #include "base/trace_event/heap_profiler_allocation_context_tracker.h"
 
 #include <algorithm>
+#include <iterator>
 
 #include "base/atomicops.h"
 #include "base/threading/thread_local_storage.h"
@@ -25,13 +26,6 @@ void DestructAllocationContextTracker(void* alloc_ctx_tracker) {
   delete static_cast<AllocationContextTracker*>(alloc_ctx_tracker);
 }
 
-// Returns a pointer past the end of the fixed-size array |array| of |T| of
-// length |N|, identical to C++11 |std::end|.
-template <typename T, int N>
-T* End(T(&array)[N]) {
-  return array + N;
-}
-
 }  // namespace
 
 AllocationContextTracker::AllocationContextTracker() {}
@@ -99,9 +93,9 @@ AllocationContext AllocationContextTracker::GetContextSnapshot() {
   // Fill the backtrace.
   {
     auto src = tracker->pseudo_stack_.begin();
-    auto dst = ctx.backtrace.frames;
+    auto dst = std::begin(ctx.backtrace.frames);
     auto src_end = tracker->pseudo_stack_.end();
-    auto dst_end = End(ctx.backtrace.frames);
+    auto dst_end = std::end(ctx.backtrace.frames);
 
     // Copy as much of the bottom of the pseudo stack into the backtrace as
     // possible.

base/trace_event/heap_profiler_allocation_context_tracker_unittest.cc

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+#include <iterator>
+
 #include "base/memory/ref_counted.h"
 #include "base/trace_event/heap_profiler_allocation_context.h"
 #include "base/trace_event/heap_profiler_allocation_context_tracker.h"
@@ -19,23 +21,16 @@ const char kEclair[] = "Eclair";
 const char kFroyo[] = "Froyo";
 const char kGingerbread[] = "Gingerbread";
 
-// Returns a pointer past the end of the fixed-size array |array| of |T| of
-// length |N|, identical to C++11 |std::end|.
-template <typename T, int N>
-const T* End(const T(&array)[N]) {
-  return array + N;
-}
-
 // Asserts that the fixed-size array |expected_backtrace| matches the backtrace
 // in |AllocationContextTracker::GetContextSnapshot|.
 template <size_t N>
 void AssertBacktraceEquals(const StackFrame(&expected_backtrace)[N]) {
   AllocationContext ctx = AllocationContextTracker::GetContextSnapshot();
 
-  auto actual = ctx.backtrace.frames;
-  auto actual_bottom = End(ctx.backtrace.frames);
-  auto expected = expected_backtrace;
-  auto expected_bottom = End(expected_backtrace);
+  auto actual = std::begin(ctx.backtrace.frames);
+  auto actual_bottom = std::end(ctx.backtrace.frames);
+  auto expected = std::begin(expected_backtrace);
+  auto expected_bottom = std::end(expected_backtrace);
 
   // Note that this requires the pointers to be equal, this is not doing a deep
   // string comparison.

styleguide/c++/c++11.html

@@ -297,6 +297,18 @@ Parameter pack</a></td>
 <td><a href="https://groups.google.com/a/chromium.org/forum/#!topic/cxx/16V7fmtbzok">Discussion thread</a>.</td>
 </tr>
 
+<tr>
+<td>Begin and End Non-Member Functions</td>
+<td><code>std::begin()</code> and <code>std::end()</code></td>
+<td>Allows use of free functions on any container, including
+fixed-size arrays</td>
+<td><a href="http://en.cppreference.com/w/cpp/iterator/begin">
+std::begin</a> and
+<a href="http://en.cppreference.com/w/cpp/iterator/end">
+std::end</a></td>
+<td>Useful for fixed-size arrays. <a href="https://groups.google.com/a/chromium.org/d/topic/cxx/5iFNE8P5qT4/discussion">Discussion thread</a></td>
+</tr>
+
 <tr>
 <td>Containers containing movable types</td>
 <td><code>vector&lt;scoped_ptr&gt;</code></td>
@@ -681,18 +693,6 @@ std::array</a></td>
 <td></td>
 </tr>
 
-<tr>
-<td>Begin and End Non-Member Functions</td>
-<td><code>std::begin()</code> and <code>std::end()</code></td>
-<td>Allows use of free functions on any container, including
-built-in arrays</td>
-<td><a href="http://en.cppreference.com/w/cpp/iterator/begin">
-std::begin</a> and
-<a href="http://en.cppreference.com/w/cpp/iterator/end">
-std::end</a></td>
-<td>Useful for built-in arrays.</td>
-</tr>
-
 <tr>
 <td>Bind Operations</td>
 <td><code>std::bind(<i>function</i>, <i>args</i>, ...)</code></td>