Add WebKitUnitTestSupport::readFromFile and deprecate all PlatformFileHandle related methods

Source/web/tests/WebImageTest.cpp

Index: Source/web/tests/WebImageTest.cpp
diff --git a/Source/web/tests/WebImageTest.cpp b/Source/web/tests/WebImageTest.cpp
index 436c999b01473e6acabb0be70dd2d05073eb5e60..24e9ffa5c23c37c86acf1c1da0824d4783bba252 100644
--- a/Source/web/tests/WebImageTest.cpp
+++ b/Source/web/tests/WebImageTest.cpp
@@ -32,7 +32,6 @@
 #include "public/platform/WebImage.h"
 
 #include <gtest/gtest.h>
-#include "core/platform/FileSystem.h"
 #include "core/platform/SharedBuffer.h"
 #include "public/platform/Platform.h"
 #include "public/platform/WebData.h"
@@ -50,16 +49,7 @@ static PassRefPtr<SharedBuffer> readFile(const char* fileName)
     filePath.append("/Source/web/tests/data/");
     filePath.append(fileName);
 
-    long long fileSize;
-    if (!getFileSize(filePath, fileSize))
-        return 0;
-
-    PlatformFileHandle handle = openFile(filePath, OpenForRead);
-    int fileLength = static_cast<int>(fileSize);
-    Vector<char> buffer(fileLength);
-    readFromFile(handle, buffer.data(), fileLength);
-    closeFile(handle);
-    return SharedBuffer::adoptVector(buffer);
+    return Platform::current()->unitTestSupport()->readFromFile(filePath);
 }
 
 TEST(WebImageTest, PNGImage)