Make SkGLContext lifetime more well-defined

tests/EGLImageTest.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "Test.h"
 #if SK_SUPPORT_GPU
 #include "GrContext.h"
@@ skipping 10 matching lines @@
             if (grbackendtex1) {
                 GrGLGpu* gpu1 = static_cast<GrGLGpu*>(grctx1->getGpu());
                 GrBackendObject handle = reinterpret_cast<GrBackendObject>(grbackendtex1);
                 gpu1->deleteTestingOnlyBackendTexture(handle, false);
             }
             grctx1->unref();
         }
         if (GR_EGL_NO_IMAGE != image1) {
             glctx1->destroyEGLImage(image1);
         }
-        glctx1->unref();
     }
 
     glctx0->makeCurrent();
     if (texID0) {
         GR_GL_CALL(glctx0->gl(), DeleteTextures(1, &texID0));
     }
 }
 
 static void test_read_pixels(skiatest::Reporter* reporter, GrContext* context,
                              GrTexture* externalTexture, uint32_t expectedPixelValues[]) {
@@ skipping 42 matching lines @@
     // extensions to run this test.
 
     if (kGLES_GrGLStandard != glCtx0->gl()->fStandard) {
         return;
     }
     GrGLGpu* gpu0 = static_cast<GrGLGpu*>(context0->getGpu());
     if (!gpu0->glCaps().externalTextureSupport()) {
         return;
     }
 
-    SkGLContext* glCtx1 = glCtx0->createNew();
+    SkAutoTDelete<SkGLContext> glCtx1 = glCtx0->createNew();
     if (!glCtx1) {
         return;
     }
     GrContext* context1 = GrContext::Create(kOpenGL_GrBackend, (GrBackendContext)glCtx1->gl());
     const GrGLTextureInfo* backendTexture1 = nullptr;
     GrEGLImage image = GR_EGL_NO_IMAGE;
     GrGLTextureInfo externalTexture;
     externalTexture.fID = 0;
 
     if (!context1) {
@@ skipping 92 matching lines @@
     test_read_pixels(reporter, context0, externalTextureObj, pixels.get());
 
     test_write_pixels(reporter, context0, externalTextureObj);
 
     test_copy_surface(reporter, context0, externalTextureObj, pixels.get());
 
     cleanup(glCtx0, externalTexture.fID, glCtx1, context1, backendTexture1, image);
 }
 
 #endif