Reland "Add more test_utils functions."

This is a reland of 5fcfcea4a9

Re-land uses static linking with angle_util. The root cause
of the CFI error wasn't solved. Static linking works around
the problem by not using any export rules.

Original change's description:
> Add more test_utils functions.
>
> Includes methods for creating temporary files, deleting files, and
> reading files into a string. Also renames GetPathSeparator to mention
> it's only used for environment variables. Includes a new virtual type
> angle::Process that will be used to implement cross-platform async
> Process launching for tests. Also includes a way to specify a custom
> crash handler callback.
>
> Also adds a few unit tests for the new functionality. They are disabled
> on Android because the functions are not needed by the new test runner.
>
> Bug: angleproject:3162
> Change-Id: I3e2c2e9837608884c98379fa0f78c9ffbe158d73
> Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1821940
> Commit-Queue: Jamie Madill <jmadill@chromium.org>
> Reviewed-by: Jonah Ryan-Davis <jonahr@google.com>

Bug: chromium:1015810
Bug: angleproject:3162
Change-Id: I6a2c1e7b585a13ca846759f32da0777c00d7f7e6
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1869541
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>

util/test_utils.cpp

@@ -0,0 +1,97 @@
+//
+// Copyright 2019 The ANGLE 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.
+//
+
+// system_utils: Defines common utility functions
+
+#include "util/test_utils.h"
+
+#include <cstring>
+#include <fstream>
+
+namespace angle
+{
+bool CreateTemporaryFile(char *tempFileNameOut, uint32_t maxFileNameLen)
+{
+    constexpr uint32_t kMaxPath = 1000u;
+    char tempPath[kMaxPath];
+
+    if (!GetTempDir(tempPath, kMaxPath))
+        return false;
+
+    return CreateTemporaryFileInDir(tempPath, tempFileNameOut, maxFileNameLen);
+}
+
+bool GetFileSize(const char *filePath, uint32_t *sizeOut)
+{
+    std::ifstream stream(filePath);
+    if (!stream)
+    {
+        return false;
+    }
+
+    stream.seekg(0, std::ios::end);
+    *sizeOut = static_cast<uint32_t>(stream.tellg());
+    return true;
+}
+
+bool ReadEntireFileToString(const char *filePath, char *contentsOut, uint32_t maxLen)
+{
+    std::ifstream stream(filePath);
+    if (!stream)
+    {
+        return false;
+    }
+
+    std::string contents;
+
+    stream.seekg(0, std::ios::end);
+    contents.reserve(static_cast<unsigned int>(stream.tellg()));
+    stream.seekg(0, std::ios::beg);
+
+    contents.assign((std::istreambuf_iterator<char>(stream)), std::istreambuf_iterator<char>());
+
+    strncpy(contentsOut, contents.c_str(), maxLen);
+    return true;
+}
+
+// static
+Process::~Process() = default;
+
+ProcessHandle::ProcessHandle() : mProcess(nullptr) {}
+
+ProcessHandle::ProcessHandle(Process *process) : mProcess(process) {}
+
+ProcessHandle::ProcessHandle(const std::vector<const char *> &args,
+                             bool captureStdout,
+                             bool captureStderr)
+    : mProcess(LaunchProcess(args, captureStdout, captureStderr))
+{}
+
+ProcessHandle::~ProcessHandle()
+{
+    reset();
+}
+
+ProcessHandle::ProcessHandle(ProcessHandle &&other) : mProcess(other.mProcess)
+{
+    other.mProcess = nullptr;
+}
+
+ProcessHandle &ProcessHandle::operator=(ProcessHandle &&rhs)
+{
+    std::swap(mProcess, rhs.mProcess);
+    return *this;
+}
+
+void ProcessHandle::reset()
+{
+    if (mProcess)
+    {
+        delete mProcess;
+        mProcess = nullptr;
+    }
+}
+}  // namespace angle