Add static asserts around assumed-static skia enum values

Protects assumptions around enums value built into LUTs

Change-Id: Ica0692e4309d50b4d3897e0f3f47809d14f786fe
diff --git a/libs/hwui/SkiaShader.cpp b/libs/hwui/SkiaShader.cpp
index 1f95946..6c105cf 100644
--- a/libs/hwui/SkiaShader.cpp
+++ b/libs/hwui/SkiaShader.cpp
@@ -32,12 +32,19 @@
 // Support
 ///////////////////////////////////////////////////////////////////////////////
 
-static const GLenum gTileModes[] = {
+static constexpr GLenum gTileModes[] = {
         GL_CLAMP_TO_EDGE,   // == SkShader::kClamp_TileMode
         GL_REPEAT,          // == SkShader::kRepeat_Mode
         GL_MIRRORED_REPEAT  // == SkShader::kMirror_TileMode
 };
 
+static_assert(gTileModes[SkShader::kClamp_TileMode] == GL_CLAMP_TO_EDGE,
+        "SkShader TileModes have changed");
+static_assert(gTileModes[SkShader::kRepeat_TileMode] == GL_REPEAT,
+        "SkShader TileModes have changed");
+static_assert(gTileModes[SkShader::kMirror_TileMode] == GL_MIRRORED_REPEAT,
+        "SkShader TileModes have changed");
+
 /**
  * This function does not work for n == 0.
  */