skia: Add support for ANGLE on linux

src/gpu/gl/angle/GrGLCreateANGLEInterface.cpp

Index: src/gpu/gl/angle/GrGLCreateANGLEInterface.cpp
diff --git a/src/gpu/gl/angle/GrGLCreateANGLEInterface.cpp b/src/gpu/gl/angle/GrGLCreateANGLEInterface.cpp
index 51e461a0d808f4f88072b987fe6dea1f446e0531..9a4dffb4b199f081c559988f95ba07fbf5047a28 100644
--- a/src/gpu/gl/angle/GrGLCreateANGLEInterface.cpp
+++ b/src/gpu/gl/angle/GrGLCreateANGLEInterface.cpp
@@ -10,12 +10,21 @@
 #include "gl/GrGLInterface.h"
 #include "gl/GrGLAssembleInterface.h"
 
+#if defined _WIN32
 #define WIN32_LEAN_AND_MEAN
 #include <windows.h>
+#else
+#include <dlfcn.h>
+#endif // defined _WIN32
+
 #include <EGL/egl.h>
 
 static GrGLFuncPtr angle_get_gl_proc(void* ctx, const char name[]) {
+#if defined _WIN32
     GrGLFuncPtr proc = (GrGLFuncPtr) GetProcAddress((HMODULE)ctx, name);
+#else
+    GrGLFuncPtr proc = (GrGLFuncPtr) dlsym(ctx, name);
+#endif // defined _WIN32
     if (proc) {
         return proc;
     }
@@ -23,17 +32,21 @@ static GrGLFuncPtr angle_get_gl_proc(void* ctx, const char name[]) {
 }
 
 const GrGLInterface* GrGLCreateANGLEInterface() {
+    static void* gANGLELib = nullptr;
 
-    static HMODULE ghANGLELib = nullptr;
-
-    if (nullptr == ghANGLELib) {
+    if (nullptr == gANGLELib) {
         // We load the ANGLE library and never let it go
-        ghANGLELib = LoadLibrary("libGLESv2.dll");
+#if defined _WIN32
+        gANGLELib = LoadLibrary("libGLESv2.dll");
+#else
+        gANGLELib = dlopen("libGLESv2.so", RTLD_LAZY);
+#endif // defined _WIN32
     }
-    if (nullptr == ghANGLELib) {
-        // We can't setup the interface correctly w/o the DLL
+
+    if (nullptr == gANGLELib) {
+        // We can't setup the interface correctly w/o the so
         return nullptr;
     }
 
-    return GrGLAssembleGLESInterface(ghANGLELib, angle_get_gl_proc);
+    return GrGLAssembleGLESInterface(gANGLELib, angle_get_gl_proc);
 }