Revert "reland 1: "mac: Run A/B experiment on SharedMemory mechanism for resource buffers.""

This reverts commit 8797516daa4b465022ee42ce57a8bb40ed53316d.

Reason: speculative revert to see if it's the cause of massive layout test
failures on MacOS 10.6 that started here:

http://build.chromium.org/p/chromium.webkit/builders/WebKit%20Mac10.6/builds/46021

BUG=547261, 466437
TBR=mark@chromium.org, isherman@chromium.org, asvitkine@chromium.org, avi@chromium.org, erikchen@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/1411573008

Cr-Commit-Position: refs/heads/master@{#356688}

3 files changed, 0 insertions, 54 deletions

diff --git a/base/memory/shared_memory.h b/base/memory/shared_memory.h
index 5cdcb0d..18416c0 100644
--- a/base/memory/shared_memory.h
+++ b/base/memory/shared_memory.h
@@ -140,10 +140,6 @@ class BASE_EXPORT SharedMemory {
   // http://crbug.com/466437.
   bool CreateAndMapAnonymousPosix(size_t size);
   bool CreateAnonymousPosix(size_t size);
-
-  // This method is an analog of CreateAndMapAnonymous that forces the
-  // underlying OS primitive to be a Mach memory object.
-  bool CreateAndMapAnonymousMach(size_t size);
 #endif  // defined(OS_MACOSX) && !defined(OS_IOS)
 
   // Creates an anonymous shared memory segment of size size.
diff --git a/base/memory/shared_memory_handle.h b/base/memory/shared_memory_handle.h
index 49398a4..b3dfc8f 100644
--- a/base/memory/shared_memory_handle.h
+++ b/base/memory/shared_memory_handle.h
@@ -75,15 +75,12 @@ class BASE_EXPORT SharedMemoryHandle {
 #else
 class BASE_EXPORT SharedMemoryHandle {
  public:
-  // The values of these enums must not change, as they are used by the
-  // histogram OSX.SharedMemory.Mechanism.
   enum Type {
     // The SharedMemoryHandle is backed by a POSIX fd.
     POSIX,
     // The SharedMemoryHandle is backed by the Mach primitive "memory object".
     MACH,
   };
-  static const int TypeMax = 2;
 
   // The format that should be used to transmit |Type| over the wire.
   typedef int TypeWireFormat;
diff --git a/base/memory/shared_memory_mac.cc b/base/memory/shared_memory_mac.cc
index 47b8a89..799b8e3 100644
--- a/base/memory/shared_memory_mac.cc
+++ b/base/memory/shared_memory_mac.cc
@@ -14,8 +14,6 @@
 #include "base/files/scoped_file.h"
 #include "base/logging.h"
 #include "base/mac/scoped_mach_vm.h"
-#include "base/metrics/field_trial.h"
-#include "base/metrics/histogram_macros.h"
 #include "base/posix/eintr_wrapper.h"
 #include "base/posix/safe_strerror.h"
 #include "base/process/process_metrics.h"
@@ -31,38 +29,6 @@ namespace base {
 
 namespace {
 
-const char kTrialName[] = "MacMemoryMechanism";
-const char kTrialMach[] = "Mach";
-const char kTrialPosix[] = "Posix";
-
-SharedMemoryHandle::Type GetABTestMechanism() {
-  static bool found_group = false;
-  static SharedMemoryHandle::Type group = SharedMemoryHandle::MACH;
-
-  if (found_group)
-    return group;
-
-  const std::string group_name =
-      base::FieldTrialList::FindFullName(kTrialName);
-  if (group_name == kTrialMach) {
-    group = SharedMemoryHandle::MACH;
-    found_group = true;
-  } else if (group_name == kTrialPosix) {
-    group = SharedMemoryHandle::POSIX;
-    found_group = true;
-  } else {
-    group = SharedMemoryHandle::MACH;
-  }
-
-  return group;
-}
-
-// Emits a histogram entry indicating which type of SharedMemory was created.
-void EmitMechanism(SharedMemoryHandle::Type type) {
-  UMA_HISTOGRAM_ENUMERATION("OSX.SharedMemory.Mechanism", type,
-                            SharedMemoryHandle::TypeMax);
-}
-
 // Returns whether the operation succeeded.
 // |new_handle| is an output variable, populated on success. The caller takes
 // ownership of the underlying memory object.
@@ -261,17 +227,6 @@ bool SharedMemory::CreateAnonymousPosix(size_t size) {
   return Create(options);
 }
 
-bool SharedMemory::CreateAndMapAnonymousMach(size_t size) {
-  SharedMemoryCreateOptions options;
-
-  // A/B test the mechanism. Once the experiment is over, this will always be
-  // set to SharedMemoryHandle::MACH.
-  // http://crbug.com/547261
-  options.type = GetABTestMechanism();
-  options.size = size;
-  return Create(options) && Map(size);
-}
-
 // static
 bool SharedMemory::GetSizeFromSharedMemoryHandle(
     const SharedMemoryHandle& handle,
@@ -293,8 +248,6 @@ bool SharedMemory::Create(const SharedMemoryCreateOptions& options) {
   if (options.size > static_cast<size_t>(std::numeric_limits<int>::max()))
     return false;
 
-  EmitMechanism(options.type);
-
   if (options.type == SharedMemoryHandle::MACH) {
     shm_ = SharedMemoryHandle(options.size);
     requested_size_ = options.size;