Use C++11 raw string literals instead of SHADER_SOURCE macro

This is better in many ways:
1. It doesn't confuse clang format
2. \n doesn't need to be included after preprocessor directives like
   the version directive.
3. It's using built-in functionality instead of something custom.

Raw string literals should be the preferred way to include shader
source in C++ files going forward.

BUG=angleproject:2157
TEST=angle_end2end_tests

Change-Id: I8b236a6e2d5c25d920297e5bc5b5b143eddeba1f
Reviewed-on: https://chromium-review.googlesource.com/671046
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>
diff --git a/src/tests/gl_tests/IncompleteTextureTest.cpp b/src/tests/gl_tests/IncompleteTextureTest.cpp
index c835676..c7f7654 100644
--- a/src/tests/gl_tests/IncompleteTextureTest.cpp
+++ b/src/tests/gl_tests/IncompleteTextureTest.cpp
@@ -28,9 +28,8 @@
     {
         ANGLETest::SetUp();
 
-        const std::string vertexShaderSource = SHADER_SOURCE
-        (
-            precision highp float;
+        const std::string vertexShaderSource =
+            R"(precision highp float;
             attribute vec4 position;
             varying vec2 texcoord;
 
@@ -38,20 +37,17 @@
             {
                 gl_Position = position;
                 texcoord = (position.xy * 0.5) + 0.5;
-            }
-        );
+            })";
 
-        const std::string fragmentShaderSource = SHADER_SOURCE
-        (
-            precision highp float;
+        const std::string fragmentShaderSource =
+            R"(precision highp float;
             uniform sampler2D tex;
             varying vec2 texcoord;
 
             void main()
             {
                 gl_FragColor = texture2D(tex, texcoord);
-            }
-        );
+            })";
 
         mProgram = CompileProgram(vertexShaderSource, fragmentShaderSource);
         if (mProgram == 0)