Add and document enable_gpu_client_logging GN argument.

This can be used in Release builds without dcheck_always_on=true, and
allows the --enable-gpu-client-logging command line argument to work.

Bug: 910783
Change-Id: I0720b7eb0c735de4d08ba50d69b41060eb387d63
Reviewed-on: https://chromium-review.googlesource.com/c/1357623Reviewed-by: Victor Miura <vmiura@chromium.org>
Commit-Queue: Kenneth Russell <kbr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#612900}

docs/gpu/debugging_gpu_related_code.md

@@ -19,6 +19,20 @@ WebGL, Skia/Ganesh, Aura), then in a debug build you can use the
 GPU service process. (From the point of view of a GPU client, it's calling
 OpenGL ES functions - but the real driver calls are made in the GPU process.)
 
+You can also use this flag in a release build by specifying the GN argument:
+
+```
+enable_gpu_client_logging=true
+```
+
+It's typically necessary to specify the `--enable-logging=stderr` flag as well:
+
+```
+--enable-gpu-client-logging --enable-logging=stderr
+```
+
+The output looks like this:
+
 ```
 [4782:4782:1219/141706:INFO:gles2_implementation.cc(1026)] [.WebGLRenderingContext] glUseProgram(3)
 [4782:4782:1219/141706:INFO:gles2_implementation_impl_autogen.h(401)] [.WebGLRenderingContext] glGenBuffers(1, 0x7fffc9e1269c)

gpu/command_buffer/client/BUILD.gn

@@ -4,6 +4,11 @@
 
 import("//build/config/jumbo.gni")
 
+declare_args() {
+  # Enable GPU client logging without DCHECK being on.
+  enable_gpu_client_logging = false
+}
+
 # The files here go into the "gpu" component in a component build (with
 # "command_buffer_client" and "gles2_cmd_helper" just forwarding) and goes into
 # separate static libraries in non-component build.
@@ -205,6 +210,9 @@ jumbo_component("gles2_implementation") {
   sources = gles2_implementation_source_files
 
   defines = [ "GLES2_IMPL_IMPLEMENTATION" ]
+  if (enable_gpu_client_logging) {
+    defines += [ "GPU_ENABLE_CLIENT_LOGGING" ]
+  }
   all_dependent_configs = [ "//third_party/khronos:khronos_headers" ]
 
   deps = [
@@ -295,6 +303,9 @@ jumbo_component("gles2_implementation_no_check") {
     "GLES2_IMPL_IMPLEMENTATION",
     "GLES2_CONFORMANCE_TESTS=1",
   ]
+  if (enable_gpu_client_logging) {
+    defines += [ "GPU_ENABLE_CLIENT_LOGGING" ]
+  }
 
   deps = [
     ":client",

gpu/command_buffer/client/logging.h

@@ -9,9 +9,15 @@
 #include "base/macros.h"
 #include "gpu/command_buffer/client/gles2_impl_export.h"
 
-// Macros to log information if DCHECK_IS_ON() and --enable-gpu-client-logging
-// flag is set. Code is optimized out if DCHECK is disabled. Requires that a
-// LogSettings named log_settings_ is in scope whenever a macro is used.
+// Macros to log information if --enable-gpu-client-logging is set and either:
+//   DCHECK_IS_ON(), or
+//   enable_gpu_client_logging=true is set in GN args.
+// Code is optimized out if DCHECK is disabled or the other GN arg is not set.
+// Requires that a LogSettings named log_settings_ is in scope whenever a macro
+// is used.
+//
+// Note that it's typically necessary to also specify --enable-logging=stderr to
+// see this logging output on Linux or macOS.
 //
 // Example usage:
 //
@@ -32,13 +38,14 @@
 //   LogSettings log_settings_;
 // };
 
-#if DCHECK_IS_ON() && !defined(__native_client__) && \
-    !defined(GLES2_CONFORMANCE_TESTS) && !defined(GLES2_INLINE_OPTIMIZATION)
+#if (DCHECK_IS_ON() || defined(GPU_ENABLE_CLIENT_LOGGING)) &&           \
+    !defined(__native_client__) && !defined(GLES2_CONFORMANCE_TESTS) && \
+    !defined(GLES2_INLINE_OPTIMIZATION)
 #define GPU_CLIENT_DEBUG
 #endif
 
 #if defined(GPU_CLIENT_DEBUG)
-#define GPU_CLIENT_LOG(args) DLOG_IF(INFO, log_settings_.enabled()) << args;
+#define GPU_CLIENT_LOG(args) LOG_IF(INFO, log_settings_.enabled()) << args;
 #define GPU_CLIENT_LOG_CODE_BLOCK(code) code
 #define GPU_CLIENT_DCHECK_CODE_BLOCK(code) code
 #else  // !defined(GPU_CLIENT_DEBUG)