Reland "OpenGL: delete shaders and pipelines when they are not used any longer"

This is a reland of a57c1db878

in current Dawn implementation RenderPipelineGL and ComputePipelineGL
will be destroyed before calling their initialize() function when we
can find a proper pipeline object in the front-end cache, so mProgram
may not be assigned to a valid GL program ID when the destructor of
PipelineGL is called.

In this CL we always initialize mProgram to 0 in the constructor of
PipelineGL so that it won't be a garbage value in the destructor of
PipelineGL (0 is safe for glDeleteProgram() according to OpenGL SPEC).

Original change's description:
> OpenGL: delete shaders and pipelines when they are not used any longer
>
> Previously on OpenGL backend the GL pipelines and shaders are never
> deleted. With this patch the GL pipelines and shaders will be able to
> be destroyed correctly after they are not needed any longer.
>
> BUG=dawn:529
>
> Change-Id: I4f7f22c7b536825363fe1ecc0f5ffd1bb86fd774
> Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/65140
> Reviewed-by: Corentin Wallez <cwallez@chromium.org>
> Reviewed-by: Stephen White <senorblanco@chromium.org>
> Commit-Queue: Jiawei Shao <jiawei.shao@intel.com>

Bug: dawn:529
Change-Id: Ie04ab069b9d26658f2b0d1b070d86bb650f3c878
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/65486
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Austin Eng <enga@chromium.org>
Reviewed-by: Stephen White <senorblanco@chromium.org>

src/dawn_native/opengl/ComputePipelineGL.cpp

@@ -27,6 +27,10 @@ namespace dawn_native { namespace opengl {
         return pipeline;
     }
 
+    ComputePipeline::~ComputePipeline() {
+        DeleteProgram(ToBackend(GetDevice())->gl);
+    }
+
     MaybeError ComputePipeline::Initialize() {
         DAWN_TRY(
             InitializeBase(ToBackend(GetDevice())->gl, ToBackend(GetLayout()), GetAllStages()));

src/dawn_native/opengl/ComputePipelineGL.h

@@ -35,7 +35,7 @@ namespace dawn_native { namespace opengl {
 
       private:
         using ComputePipelineBase::ComputePipelineBase;
-        ~ComputePipeline() override = default;
+        ~ComputePipeline() override;
         MaybeError Initialize() override;
     };
 

src/dawn_native/opengl/PipelineGL.cpp

@@ -45,7 +45,9 @@ namespace dawn_native { namespace opengl {
 
     }  // namespace
 
-    PipelineGL::PipelineGL() = default;
+    PipelineGL::PipelineGL() : mProgram(0) {
+    }
+
     PipelineGL::~PipelineGL() = default;
 
     MaybeError PipelineGL::InitializeBase(const OpenGLFunctions& gl,
@@ -87,6 +89,7 @@ namespace dawn_native { namespace opengl {
         // Create an OpenGL shader for each stage and gather the list of combined samplers.
         PerStage<CombinedSamplerInfo> combinedSamplers;
         bool needsDummySampler = false;
+        std::vector<GLuint> glShaders;
         for (SingleShaderStage stage : IterateStages(activeStages)) {
             const ShaderModule* module = ToBackend(stages[stage].module.Get());
             std::string glsl;
@@ -96,6 +99,7 @@ namespace dawn_native { namespace opengl {
             GLuint shader;
             DAWN_TRY_ASSIGN(shader, CreateShader(gl, GLShaderType(stage), glsl.c_str()));
             gl.AttachShader(mProgram, shader);
+            glShaders.push_back(shader);
         }
 
         if (needsDummySampler) {
@@ -178,9 +182,19 @@ namespace dawn_native { namespace opengl {
 
             textureUnit++;
         }
+
+        for (GLuint glShader : glShaders) {
+            gl.DetachShader(mProgram, glShader);
+            gl.DeleteShader(glShader);
+        }
+
         return {};
     }
 
+    void PipelineGL::DeleteProgram(const OpenGLFunctions& gl) {
+        gl.DeleteProgram(mProgram);
+    }
+
     const std::vector<PipelineGL::SamplerUnit>& PipelineGL::GetTextureUnitsForSampler(
         GLuint index) const {
         ASSERT(index < mUnitsForSamplers.size());

src/dawn_native/opengl/PipelineGL.h

@@ -47,12 +47,12 @@ namespace dawn_native { namespace opengl {
         const std::vector<GLuint>& GetTextureUnitsForTextureView(GLuint index) const;
         GLuint GetProgramHandle() const;
 
-        void ApplyNow(const OpenGLFunctions& gl);
-
       protected:
+        void ApplyNow(const OpenGLFunctions& gl);
         MaybeError InitializeBase(const OpenGLFunctions& gl,
                                   const PipelineLayout* layout,
                                   const PerStage<ProgrammableStage>& stages);
+        void DeleteProgram(const OpenGLFunctions& gl);
 
       private:
         GLuint mProgram;

src/dawn_native/opengl/RenderPipelineGL.cpp

@@ -238,6 +238,7 @@ namespace dawn_native { namespace opengl {
         const OpenGLFunctions& gl = ToBackend(GetDevice())->gl;
         gl.DeleteVertexArrays(1, &mVertexArrayObject);
         gl.BindVertexArray(0);
+        DeleteProgram(gl);
     }
 
     GLenum RenderPipeline::GetGLPrimitiveTopology() const {