In the current LoadNativeLibrary implementation, LoadLibraryW Windows
API is used to load a DLL. To be able to find dependencies in the same
folder, SetCurrentDirectory() is needed to search for the DLL directory,
and sets it back after the DLL is loaded. This is required because on
Windows, it'll search for dependencies in a search list, which includes
the system "current directory", but not the DLL directory.

However, SetCurrentDirectory() can be potentially problematic. It is not
recommended in a multithreaded application, and could pose a security
risk as "If an attacker gains control of one of the directories on the
DLL search path, it can place a malicious copy of the DLL in that
directory. This is sometimes called a DLL preloading attack or a binary
planting attack."

The right thing to do is to use LoadLibraryExW, where we can specify
additional flags like LOAD_LIBRARY_SEARCH_DLL_LOAD_DIR to enable
searching in the DLL directory. With this, we can eliminate the need of
doing SetCurrentDirectory().

Using these additional flags requires KB2533623 to be installed and the
method is "To determine whether the flags are available, use
GetProcAddress to get the address of the AddDllDirectory,
RemoveDllDirectory, or SetDefaultDllDirectories function. If
GetProcAddress succeeds, the LOAD_LIBRARY_SEARCH_* flags can be used
with LoadLibraryEx."

Therefore, we can dynamically call LoadLibraryExW if the API and the
flags are available. If not or its call fails, we should use the
LoadLibraryW API.

This CL also adds UMA histogram to record the calling status of both
LoadLibraryExW and LoadLibraryW APIs. Besides, this CL removes the
LoadNativeLibraryDynamically method as it is not used anywhere.

Running Chromium built with this CL locally shows that LoadLibraryExW
call were successful for kernel32.dll and widevinecdm.dll (which caused
crbug.com/700208), but failed when loading MDMRegistration.dll.
LoadLibraryW succeeds in loading MDMRegistration.dll though.

BUG=700503,700208

Review-Url: https://codereview.chromium.org/2744043003
Cr-Commit-Position: refs/heads/master@{#457359}