Pass std::string_view by value not by ref (flutter#33699)

String views are small, cheap objects that fit in a couple registers, so
passing by value avoids pointer indirection and thus a memory load.

Fun related reading for future archaeologists:
https://quuxplusone.github.io/blog/2021/11/09/pass-string-view-by-value/

And a Windows-specific footnote:
https://quuxplusone.github.io/blog/2021/11/19/string-view-by-value-ps/

No test change since there is no semantic change.

Author: cbracken

impeller/compiler/reflector.cc

@@ -304,7 +304,7 @@ static std::string ToString(CompilerBackend::Type type) {
 }
 
 std::shared_ptr<fml::Mapping> Reflector::InflateTemplate(
-    const std::string_view& tmpl) const {
+    std::string_view tmpl) const {
   inja::Environment env;
   env.set_trim_blocks(true);
   env.set_lstrip_blocks(true);

impeller/compiler/reflector.h

@@ -91,8 +91,7 @@ class Reflector {
 
   std::shared_ptr<fml::Mapping> GenerateReflectionCC() const;
 
-  std::shared_ptr<fml::Mapping> InflateTemplate(
-      const std::string_view& tmpl) const;
+  std::shared_ptr<fml::Mapping> InflateTemplate(std::string_view tmpl) const;
 
   std::optional<nlohmann::json::object_t> ReflectResource(
       const spirv_cross::Resource& resource) const;

impeller/renderer/backend/gles/shader_library_gles.cc

@@ -94,7 +94,7 @@ bool ShaderLibraryGLES::IsValid() const {
 
 // |ShaderLibrary|
 std::shared_ptr<const ShaderFunction> ShaderLibraryGLES::GetFunction(
-    const std::string_view& name,
+    std::string_view name,
     ShaderStage stage) {
   const auto key = ShaderKey{name, stage};
   if (auto found = functions_.find(key); found != functions_.end()) {

impeller/renderer/backend/gles/shader_library_gles.h

@@ -30,9 +30,8 @@ class ShaderLibraryGLES final : public ShaderLibrary {
       std::vector<std::shared_ptr<fml::Mapping>> shader_libraries);
 
   // |ShaderLibrary|
-  std::shared_ptr<const ShaderFunction> GetFunction(
-      const std::string_view& name,
-      ShaderStage stage) override;
+  std::shared_ptr<const ShaderFunction> GetFunction(std::string_view name,
+                                                    ShaderStage stage) override;
 
   FML_DISALLOW_COPY_AND_ASSIGN(ShaderLibraryGLES);
 };

impeller/renderer/backend/gles/texture_gles.cc

@@ -79,7 +79,7 @@ bool TextureGLES::IsValid() const {
 }
 
 // |Texture|
-void TextureGLES::SetLabel(const std::string_view& label) {
+void TextureGLES::SetLabel(std::string_view label) {
   reactor_->SetDebugLabel(handle_, std::string{label.data(), label.size()});
 }
 

impeller/renderer/backend/gles/texture_gles.h

@@ -62,7 +62,7 @@ class TextureGLES final : public Texture,
               bool is_wrapped);
 
   // |Texture|
-  void SetLabel(const std::string_view& label) override;
+  void SetLabel(std::string_view label) override;
 
   // |Texture|
   bool OnSetContents(const uint8_t* contents,

impeller/renderer/backend/metal/shader_library_mtl.h

@@ -39,9 +39,8 @@ class ShaderLibraryMTL final : public ShaderLibrary {
   ShaderLibraryMTL(NSArray<id<MTLLibrary>>* libraries);
 
   // |ShaderLibrary|
-  std::shared_ptr<const ShaderFunction> GetFunction(
-      const std::string_view& name,
-      ShaderStage stage) override;
+  std::shared_ptr<const ShaderFunction> GetFunction(std::string_view name,
+                                                    ShaderStage stage) override;
 
   FML_DISALLOW_COPY_AND_ASSIGN(ShaderLibraryMTL);
 };

impeller/renderer/backend/metal/shader_library_mtl.mm

@@ -24,7 +24,7 @@
 }
 
 std::shared_ptr<const ShaderFunction> ShaderLibraryMTL::GetFunction(
-    const std::string_view& name,
+    std::string_view name,
     ShaderStage stage) {
   if (!IsValid()) {
     return nullptr;

impeller/renderer/backend/metal/texture_mtl.h

@@ -27,7 +27,7 @@ class TextureMTL final : public Texture,
   bool is_valid_ = false;
 
   // |Texture|
-  void SetLabel(const std::string_view& label) override;
+  void SetLabel(std::string_view label) override;
 
   // |Texture|
   bool OnSetContents(const uint8_t* contents,

impeller/renderer/backend/metal/texture_mtl.mm

@@ -26,7 +26,7 @@
 
 TextureMTL::~TextureMTL() = default;
 
-void TextureMTL::SetLabel(const std::string_view& label) {
+void TextureMTL::SetLabel(std::string_view label) {
   [texture_ setLabel:@(label.data())];
 }