Fix Android multi-process tests on M.

On M, there are two issues:
1. Fd 4 is important, although I don't know what it is.
2. Some test environment setup can't be done in the child process.

BUG=608732,585849

Review-Url: https://codereview.chromium.org/1952513003
Cr-Commit-Position: refs/heads/master@{#391692}

base/posix/global_descriptors.h

@@ -55,7 +55,9 @@ class BASE_EXPORT GlobalDescriptors {
 #if !defined(OS_ANDROID)
   static const int kBaseDescriptor = 3;  // 0, 1, 2 are already taken.
 #else
-  static const int kBaseDescriptor = 4;  // 3 used by __android_log_write().
+  // 3 used by __android_log_write().
+  // 4 used by... something important on Android M.
+  static const int kBaseDescriptor = 5;
 #endif
 
   // Return the singleton instance of GlobalDescriptors.

base/test/multiprocess_test.h

@@ -74,6 +74,9 @@ CommandLine GetMultiProcessTestChildBaseCommandLine();
 // component builds.
 void InitAndroidMultiProcessTestHelper(int (*main)(int, char**));
 
+// Returns true if the current process is a test child.
+bool AndroidIsChildProcess();
+
 // Wait for a test child to exit if the alternate test child implementation is
 // being used.
 bool AndroidWaitForChildExitWithTimeout(

base/test/multiprocess_test_android.cc

@@ -103,7 +103,7 @@ class LaunchHelper {
                                    int* exit_code);
 
   bool IsReady() const { return child_fd_ != -1; }
-  bool IsChild() const { return parent_fd_ != -1; }
+  bool IsChild() const { return is_child_; }
 
  private:
   // Wrappers around sendmsg/recvmsg that supports message fragmentation.
@@ -119,6 +119,8 @@ class LaunchHelper {
                            std::vector<ScopedFD> fds);
   void WaitForChildInHelper(const WaitProcessRequest* request);
 
+  bool is_child_ = false;
+
   // Parent vars.
   int child_fd_ = -1;
 
@@ -204,6 +206,7 @@ void LaunchHelper::DoParent(int fd) {
 
 void LaunchHelper::DoHelper(int fd) {
   parent_fd_ = fd;
+  is_child_ = true;
   std::unique_ptr<char[]> buf(new char[kMaxMessageSize]);
   while (true) {
     // Wait for a message from the parent.
@@ -247,6 +250,7 @@ void LaunchHelper::StartProcessInHelper(const StartProcessRequest* request,
   } else {
     // Child.
     PCHECK(close(parent_fd_) == 0);
+    parent_fd_ = -1;
     CommandLine::Reset();
 
     Pickle serialised_extra(reinterpret_cast<const char*>(request + 1),
@@ -264,10 +268,12 @@ void LaunchHelper::StartProcessInHelper(const StartProcessRequest* request,
       int new_fd;
       CHECK(iter.ReadInt(&new_fd));
       int old_fd = fds[i].release();
-      if (dup2(old_fd, new_fd) < 0) {
-        PLOG(FATAL) << "dup2";
+      if (new_fd != old_fd) {
+        if (dup2(old_fd, new_fd) < 0) {
+          PLOG(FATAL) << "dup2";
+        }
+        PCHECK(close(old_fd) == 0);
       }
-      PCHECK(close(old_fd) == 0);
     }
 
     std::unique_ptr<char*[]> argv(new char*[args.size()]);
@@ -370,6 +376,10 @@ void InitAndroidMultiProcessTestHelper(int (*main)(int, char**)) {
   g_launch_helper.Get().Init(main);
 }
 
+bool AndroidIsChildProcess() {
+  return g_launch_helper.Get().IsChild();
+}
+
 bool AndroidWaitForChildExitWithTimeout(
     const Process& process, TimeDelta timeout, int* exit_code) {
   CHECK(g_launch_helper.Get().IsReady());

base/test/test_support_android.cc

@@ -14,6 +14,7 @@
 #include "base/message_loop/message_pump_android.h"
 #include "base/path_service.h"
 #include "base/synchronization/waitable_event.h"
+#include "base/test/multiprocess_test.h"
 
 namespace {
 
@@ -176,8 +177,10 @@ void InitAndroidTestMessageLoop() {
 }
 
 void InitAndroidTest() {
-  InitAndroidTestLogging();
-  InitAndroidTestPaths();
+  if (!base::AndroidIsChildProcess()) {
+    InitAndroidTestLogging();
+    InitAndroidTestPaths();
+  }
   InitAndroidTestMessageLoop();
 }
 }  // namespace base