Service Manager: Override DLL search path when launching services in component builds

Service executables don't live alongside other build artifacts, so in component builds
Windows doesn't normally know where to look for them at runtime. This overrides the
DLL search path temporarily before launching any service child process.

BUG=None
R=ben@chromium.org

Review-Url: https://codereview.chromium.org/2574653002
Cr-Commit-Position: refs/heads/master@{#438086}

services/service_manager/runner/host/child_process_host.cc

@@ -11,6 +11,7 @@
 #include "base/base_paths.h"
 #include "base/bind.h"
 #include "base/command_line.h"
+#include "base/files/file_path.h"
 #include "base/location.h"
 #include "base/logging.h"
 #include "base/macros.h"
@@ -41,6 +42,28 @@
 #include "services/service_manager/public/cpp/standalone_service/mach_broker.h"
 #endif
 
+#if defined(OS_WIN) && defined(COMPONENT_BUILD)
+#include <windows.h>
+
+namespace {
+
+class ScopedDllDirectoryOverride {
+ public:
+  explicit ScopedDllDirectoryOverride(const base::FilePath& path) {
+    SetDllDirectory(path.value().c_str());
+  }
+
+  ~ScopedDllDirectoryOverride() {
+    SetDllDirectory(NULL);
+  }
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(ScopedDllDirectoryOverride);
+};
+
+}  // namespace
+#endif  // defined(OS_WIN) && defined(COMPONENT_BUILD)
+
 namespace service_manager {
 
 ChildProcessHost::ChildProcessHost(base::TaskRunner* launch_process_runner,
@@ -205,6 +228,8 @@ void ChildProcessHost::DoLaunch(
 #if defined(OS_MACOSX)
     MachBroker* mach_broker = MachBroker::GetInstance();
     base::AutoLock locker(mach_broker->GetLock());
+#elif defined(OS_WIN) && defined(COMPONENT_BUILD)
+    ScopedDllDirectoryOverride dll_override(exe_dir);
 #endif
     child_process_ = base::LaunchProcess(*child_command_line, options);
 #if defined(OS_MACOSX)