Add Instant Trace Event for shader compilation in gpu which outputs shader text as attribute

BUG=skia:
R=bsalomon@google.com

Author: egdaniel@google.com

Review URL: https://codereview.chromium.org/368943002

src/gpu/gl/GrGLShaderBuilder.cpp

@@ -767,6 +767,9 @@ static GrGLuint attach_shader(const GrGLContext& glCtx,
             return 0;
         }
     }
+
+    TRACE_EVENT_INSTANT1(TRACE_DISABLED_BY_DEFAULT("skia.gpu"), "skia_gpu::GLShader",
+                         TRACE_EVENT_SCOPE_THREAD, "shader", TRACE_STR_COPY(shaderSrc.c_str()));
     if (c_PrintShaders) {
         GrPrintf(shaderSrc.c_str());
         GrPrintf("\n");