Reland of Split iOS sdk in to separate targets (patchset #1 id:1 of https://codereview.webrtc.org/2890513002/ )

Reason for revert:
Fixing downstream breakages

Original issue's description:
> Revert of Split iOS sdk in to separate targets (patchset #13 id:280001 of https://codereview.webrtc.org/2862543002/ )
>
> Reason for revert:
> Breaking downstream projects.
>
> Original issue's description:
> > Split iOS sdk in to separate targets
> >
> > This CL splits the iOS sdk into separate static libraries for video,
> > audio, ui, common, and peerconnection-related code. This will in the
> > future make it easier to compile WebRTC without unneeded components.
> >
> > BUG=webrtc:4867
> >
> > Review-Url: https://codereview.webrtc.org/2862543002
> > Cr-Commit-Position: refs/heads/master@{#18166}
> > Committed: 52c83fe710
>
> TBR=magjed@webrtc.org,denicija@webrtc.org,tkchin@webrtc.org,henrika@webrtc.org,kthelgason@webrtc.org
> # Skipping CQ checks because original CL landed less than 1 days ago.
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=webrtc:4867
>
> Review-Url: https://codereview.webrtc.org/2890513002
> Cr-Commit-Position: refs/heads/master@{#18170}
> Committed: 9756238084

TBR=magjed@webrtc.org,denicija@webrtc.org,tkchin@webrtc.org,henrika@webrtc.org,charujain@webrtc.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=webrtc:4867

Review-Url: https://codereview.webrtc.org/2890733003
Cr-Commit-Position: refs/heads/master@{#18174}

webrtc/sdk/objc/Framework/Classes/Common/helpers.mm

@@ -0,0 +1,135 @@
+/*
+ *  Copyright (c) 2015 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+
+#import <Foundation/Foundation.h>
+#import <sys/sysctl.h>
+#if defined(WEBRTC_IOS)
+#import <UIKit/UIKit.h>
+#endif
+
+#include <memory>
+
+#include "webrtc/base/checks.h"
+#include "webrtc/base/logging.h"
+#include "webrtc/sdk/objc/Framework/Classes/Common/helpers.h"
+
+namespace webrtc {
+namespace ios {
+
+#if defined(WEBRTC_IOS)
+bool isOperatingSystemAtLeastVersion(double version) {
+  return GetSystemVersion() >= version;
+}
+#endif
+
+NSString* NSStringFromStdString(const std::string& stdString) {
+  // std::string may contain null termination character so we construct
+  // using length.
+  return [[NSString alloc] initWithBytes:stdString.data()
+                                  length:stdString.length()
+                                encoding:NSUTF8StringEncoding];
+}
+
+std::string StdStringFromNSString(NSString* nsString) {
+  NSData* charData = [nsString dataUsingEncoding:NSUTF8StringEncoding];
+  return std::string(reinterpret_cast<const char*>([charData bytes]),
+                     [charData length]);
+}
+
+bool CheckAndLogError(BOOL success, NSError* error) {
+  if (!success) {
+    NSString* msg =
+        [NSString stringWithFormat:@"Error: %ld, %@, %@", (long)error.code,
+                                   error.localizedDescription,
+                                   error.localizedFailureReason];
+    LOG(LS_ERROR) << StdStringFromNSString(msg);
+    return false;
+  }
+  return true;
+}
+
+// TODO(henrika): see if it is possible to move to GetThreadName in
+// platform_thread.h and base it on pthread methods instead.
+std::string GetCurrentThreadDescription() {
+  NSString* name = [NSString stringWithFormat:@"%@", [NSThread currentThread]];
+  return StdStringFromNSString(name);
+}
+
+#if defined(WEBRTC_IOS)
+std::string GetSystemName() {
+  NSString* osName = [[UIDevice currentDevice] systemName];
+  return StdStringFromNSString(osName);
+}
+
+std::string GetSystemVersionAsString() {
+  NSString* osVersion = [[UIDevice currentDevice] systemVersion];
+  return StdStringFromNSString(osVersion);
+}
+
+double GetSystemVersion() {
+  static dispatch_once_t once_token;
+  static double system_version;
+  dispatch_once(&once_token, ^{
+    system_version = [UIDevice currentDevice].systemVersion.doubleValue;
+  });
+  return system_version;
+}
+
+std::string GetDeviceType() {
+  NSString* deviceModel = [[UIDevice currentDevice] model];
+  return StdStringFromNSString(deviceModel);
+}
+#endif
+
+std::string GetDeviceName() {
+  size_t size;
+  sysctlbyname("hw.machine", NULL, &size, NULL, 0);
+  std::unique_ptr<char[]> machine;
+  machine.reset(new char[size]);
+  sysctlbyname("hw.machine", machine.get(), &size, NULL, 0);
+  return std::string(machine.get());
+}
+
+std::string GetProcessName() {
+  NSString* processName = [NSProcessInfo processInfo].processName;
+  return StdStringFromNSString(processName);
+}
+
+int GetProcessID() {
+  return [NSProcessInfo processInfo].processIdentifier;
+}
+
+std::string GetOSVersionString() {
+  NSString* osVersion =
+      [NSProcessInfo processInfo].operatingSystemVersionString;
+  return StdStringFromNSString(osVersion);
+}
+
+int GetProcessorCount() {
+  return [NSProcessInfo processInfo].processorCount;
+}
+
+#if defined(__IPHONE_9_0) && defined(__IPHONE_OS_VERSION_MAX_ALLOWED) \
+    && __IPHONE_OS_VERSION_MAX_ALLOWED >= __IPHONE_9_0
+bool GetLowPowerModeEnabled() {
+  if (isOperatingSystemAtLeastVersion(9.0)) {
+    // lowPoweredModeEnabled is only available on iOS9+.
+    return [NSProcessInfo processInfo].lowPowerModeEnabled;
+  }
+  LOG(LS_WARNING) << "webrtc::ios::GetLowPowerModeEnabled() is not "
+                     "supported. Requires at least iOS 9.0";
+  return false;
+}
+#endif
+
+}  // namespace ios
+}  // namespace webrtc
+