Add a snapshot of flutter/engine/src/build to our sdk

build/config/compiler/BUILD.gn

+# Copyright (c) 2013 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+import("//build/config/android/config.gni")
+import("//build/config/chrome_build.gni")
+if (current_cpu == "arm") {
+  import("//build/config/arm.gni")
+}
+if (current_cpu == "mipsel" || current_cpu == "mips64el") {
+  import("//build/config/mips.gni")
+}
+if (is_posix) {
+  import("//build/config/gcc/gcc_version.gni")
+}
+if (is_win) {
+  import("//build/config/win/visual_studio_version.gni")
+}
+
+import("//build/toolchain/ccache.gni")
+import("//build/config/sanitizers/sanitizers.gni")
+
+declare_args() {
+  # Normally, Android builds are lightly optimized, even for debug builds, to
+  # keep binary size down. Setting this flag to true disables such optimization
+  android_full_debug = false
+
+  # Whether to use the binary binutils checked into third_party/binutils.
+  # These are not multi-arch so cannot be used except on x86 and x86-64 (the
+  # only two architectures that are currently checked in). Turn this off when
+  # you are using a custom toolchain and need to control -B in cflags.
+  linux_use_bundled_binutils = is_linux && current_cpu == "x64"
+
+  # Compile in such a way as to enable profiling of the generated code. For
+  # example, don't omit the frame pointer and leave in symbols.
+  enable_profiling = false
+
+  # Compile in such a way as to make it possible for the profiler to unwind full
+  # stack frames. Setting this flag has a large effect on the performance of the
+  # generated code than just setting profiling, but gives the profiler more
+  # information to analyze.
+  # Requires profiling to be set to true.
+  enable_full_stack_frames_for_profiling = false
+
+  # Use gold for linking on 64-bit Linux only (on 32-bit it runs out of
+  # address space, and it doesn't support cross-compiling).
+  use_gold = is_linux && current_cpu == "x64"
+
+  # use_debug_fission: whether to use split DWARF debug info
+  # files. This can reduce link time significantly, but is incompatible
+  # with some utilities such as icecc and ccache. Requires gold and
+  # gcc >= 4.8 or clang.
+  # http://gcc.gnu.org/wiki/DebugFission
+  use_debug_fission = is_debug && !is_win && use_gold &&
+                      linux_use_bundled_binutils && !use_ccache
+
+  if (is_win) {
+    # Whether the VS xtree header has been patched to disable warning 4702. If
+    # it has, then we don't need to disable 4702 (unreachable code warning).
+    # The patch is preapplied to the internal toolchain and hence all bots.
+    msvs_xtree_patched = false
+  }
+}
+
+# default_include_dirs ---------------------------------------------------------
+#
+# This is a separate config so that third_party code (which would not use the
+# source root and might have conflicting versions of some headers) can remove
+# this and specify their own include paths.
+config("default_include_dirs") {
+  include_dirs = [
+    "//",
+    root_gen_dir,
+  ]
+}
+
+# TODO(GYP): is_ubsan, is_ubsan_vptr
+if (!is_win) {
+  using_sanitizer = is_asan || is_lsan || is_tsan || is_msan
+}
+
+# compiler ---------------------------------------------------------------------
+#
+# Base compiler configuration.
+#
+# See also "runtime_library" below for related stuff and a discussion about
+# where stuff should go. Put warning related stuff in the "warnings" config.
+
+config("compiler") {
+  cflags = []
+  cflags_c = []
+  cflags_cc = []
+  cflags_objcc = []
+  ldflags = []
+  defines = []
+
+  # In general, Windows is totally different, but all the other builds share
+  # some common GCC configuration. This section sets up Windows and the common
+  # GCC flags, and then we handle the other non-Windows platforms specifically
+  # below.
+  if (is_win) {
+    # Windows compiler flags setup.
+    # -----------------------------
+    cflags += [
+      "/Gy",  # Enable function-level linking.
+      "/GS",  # Enable buffer security checking.
+      "/FS",  # Preserve previous PDB behavior.
+    ]
+
+    # Building with Clang on Windows is a work in progress and very
+    # experimental. See crbug.com/82385.
+    # Keep this in sync with the similar block in build/common.gypi
+    if (is_clang) {
+      cflags += [
+        # Many files use intrinsics without including this header.
+        # TODO(hans): Fix those files, or move this to sub-GYPs.
+        "/FIIntrin.h",
+      ]
+
+      if (visual_studio_version == "2013") {
+        cflags += [ "-fmsc-version=1800" ]
+      } else if (visual_studio_version == "2015") {
+        cflags += [ "-fmsc-version=1900" ]
+      }
+
+      if (current_cpu == "x86") {
+        cflags += [
+          "/fallback",
+          "-m32",
+        ]
+      } else {
+        cflags += [ "-m64" ]
+      }
+      if (exec_script("//build/win/use_ansi_codes.py", [], "trim string") ==
+          "True") {
+        cflags += [
+          # cmd.exe doesn't understand ANSI escape codes by default,
+          # so only enable them if something emulating them is around.
+          "-fansi-escape-codes",
+        ]
+      }
+    }
+  } else {
+    # Common GCC compiler flags setup.
+    # --------------------------------
+    cflags += [ "-fno-strict-aliasing" ]  # See http://crbug.com/32204
+    common_flags = [
+      # Not exporting C++ inline functions can generally be applied anywhere
+      # so we do so here. Normal function visibility is controlled by
+      # //build/config/gcc:symbol_visibility_hidden.
+      "-fvisibility-inlines-hidden",
+    ]
+    cflags_cc += common_flags
+    cflags_objcc += common_flags
+
+    # Stack protection.
+    if (is_mac) {
+      cflags += [ "-fstack-protector-all" ]
+    } else if (is_linux) {
+      cflags += [
+        "-fstack-protector",
+        "--param=ssp-buffer-size=4",
+      ]
+    }
+
+    # Linker warnings.
+    if (!(is_chromeos && current_cpu == "arm") && !is_mac && !is_ios) {
+      # TODO(jochen): Enable this on chromeos on arm. http://crbug.com/356580
+      ldflags += [ "-Wl,--fatal-warnings" ]
+    }
+
+    # Common options for AddressSanitizer, LeakSanitizer, ThreadSanitizer and
+    # MemorySanitizer
+    if (using_sanitizer) {
+      cflags += [
+        "-fno-omit-frame-pointer",
+        "-gline-tables-only",
+      ]
+    }
+    if (is_asan) {
+      asan_blacklist_path =
+          rebase_path("//tools/memory/asan/blacklist.txt", root_build_dir)
+      cflags += [
+        "-fsanitize=address",
+        "-fsanitize-blacklist=$asan_blacklist_path",
+      ]
+      if (is_mac) {
+        cflags += [ "-mllvm -asan-globals=0" ]  # http://crbug.com/352073
+        # TODO(GYP): deal with mac_bundles.
+      }
+    }
+    if (is_lsan) {
+      cflags += [ "-fsanitize=leak" ]
+    }
+    if (is_tsan) {
+      tsan_blacklist_path =
+          rebase_path("//tools/memory/tsan_v2/ignores.txt", root_build_dir)
+      cflags += [
+        "-fsanitize=thread",
+        "-fsanitize-blacklist=$tsan_blacklist_path",
+      ]
+    }
+    if (is_msan) {
+      msan_blacklist_path =
+          rebase_path("//tools/msan/blacklist.txt", root_build_dir)
+      cflags += [
+        "-fsanitize=memory",
+        "-fsanitize-memory-track-origins=$msan_track_origins",
+        "-fsanitize-blacklist=$msan_blacklist_path",
+      ]
+    }
+
+    if (use_custom_libcxx) {
+      cflags_cc += [ "-nostdinc++" ]
+      include_dirs = [
+        "//buildtools/third_party/libc++/trunk/include",
+        "//buildtools/third_party/libc++abi/trunk/include",
+      ]
+    }
+
+    if (is_fnl) {
+      # TODO(kulakowski) remove when fnl no longer uses gcc
+      cflags += [ "-Wno-maybe-uninitialized" ]
+    }
+  }
+
+  if (is_clang && is_debug) {
+    # Allow comparing the address of references and 'this' against 0
+    # in debug builds. Technically, these can never be null in
+    # well-defined C/C++ and Clang can optimize such checks away in
+    # release builds, but they may be used in asserts in debug builds.
+    extra_flags = [
+      "-Wno-undefined-bool-conversion",
+      "-Wno-tautological-undefined-compare",
+    ]
+    cflags_cc += extra_flags
+    cflags_objcc += extra_flags
+  }
+
+  if (is_clang && !is_nacl) {
+    # This is here so that all files get recompiled after a clang roll and
+    # when turning clang on or off. (defines are passed via the command line,
+    # and build system rebuild things when their commandline changes). Nothing
+    # should ever read this define.
+    defines +=
+        [ "CR_CLANG_REVISION=" + exec_script("//tools/clang/scripts/update.py",
+                                             [ "--print-revision" ],
+                                             "trim string") ]
+  }
+
+  # Mac-specific compiler flags setup.
+  # ----------------------------------
+  if (is_mac || is_ios) {
+    # These flags are shared between the C compiler and linker.
+    common_mac_flags = []
+
+    # CPU architecture.
+    if (current_cpu == "x64") {
+      common_mac_flags += [
+        "-arch",
+        "x86_64",
+      ]
+    } else if (current_cpu == "x86") {
+      common_mac_flags += [
+        "-arch",
+        "i386",
+      ]
+    } else if (current_cpu == "arm") {
+      common_mac_flags += [
+        "-arch",
+        "armv7",
+      ]
+    } else if (current_cpu == "arm64") {
+      common_mac_flags += [
+        "-arch",
+        "arm64",
+      ]
+    }
+
+    cflags += common_mac_flags
+
+    # Without this, the constructors and destructors of a C++ object inside
+    # an Objective C struct won't be called, which is very bad.
+    cflags_objcc += [ "-fobjc-call-cxx-cdtors" ]
+
+    cflags_c += [ "-std=c99" ]
+
+    ldflags += common_mac_flags
+  } else if (is_posix) {
+    # CPU architecture. We may or may not be doing a cross compile now, so for
+    # simplicity we always explicitly set the architecture.
+    if (current_cpu == "x64") {
+      cflags += [
+        "-m64",
+        "-march=x86-64",
+      ]
+      ldflags += [ "-m64" ]
+    } else if (current_cpu == "x86") {
+      cflags += [ "-m32" ]
+      ldflags += [ "-m32" ]
+      if (is_clang) {
+        cflags += [
+          # Else building libyuv gives clang's register allocator issues,
+          # see llvm.org/PR15798 / crbug.com/233709
+          "-momit-leaf-frame-pointer",
+
+          # Align the stack on 16-byte boundaries, http://crbug.com/418554.
+          "-mstack-alignment=16",
+          "-mstackrealign",
+        ]
+      }
+    } else if (current_cpu == "arm") {
+      cflags += [
+        "-march=$arm_arch",
+        "-mfloat-abi=$arm_float_abi",
+      ]
+      if (arm_tune != "") {
+        cflags += [ "-mtune=$arm_tune" ]
+      }
+      if (arm_use_thumb) {
+        cflags += [ "-mthumb" ]
+        if (is_android && !is_clang) {  # Clang doesn't support this option.
+          cflags += [ "-mthumb-interwork" ]
+        }
+      }
+      if (!is_clang) {
+        # Clang doesn't support these flags.
+        cflags += [
+          # The tree-sra optimization (scalar replacement for
+          # aggregates enabling subsequent optimizations) leads to
+          # invalid code generation when using the Android NDK's
+          # compiler (r5-r7). This can be verified using
+          # webkit_unit_tests' WTF.Checked_int8_t test.
+          "-fno-tree-sra",
+
+          # The following option is disabled to improve binary
+          # size and performance in gcc 4.9.
+          "-fno-caller-saves",
+        ]
+      }
+    } else if (current_cpu == "mipsel") {
+      if (mips_arch_variant == "r6") {
+        cflags += [
+          "-mips32r6",
+          "-Wa,-mips32r6",
+        ]
+        if (is_android) {
+          ldflags += [
+            "-mips32r6",
+            "-Wl,-melf32ltsmip",
+          ]
+        }
+      } else if (mips_arch_variant == "r2") {
+        cflags += [
+          "-mips32r2",
+          "-Wa,-mips32r2",
+        ]
+        if (mips_float_abi == "hard" && mips_fpu_mode != "") {
+          cflags += [ "-m$mips_fpu_mode" ]
+        }
+      } else if (mips_arch_variant == "r1") {
+        cflags += [
+          "-mips32",
+          "-Wa,-mips32",
+        ]
+      }
+
+      if (mips_dsp_rev == 1) {
+        cflags += [ "-mdsp" ]
+      } else if (mips_dsp_rev == 2) {
+        cflags += [ "-mdspr2" ]
+      }
+
+      cflags += [ "-m${mips_float_abi}-float" ]
+    } else if (current_cpu == "mips64el") {
+      if (mips_arch_variant == "r6") {
+        cflags += [
+          "-mips64r6",
+          "-Wa,-mips64r6",
+        ]
+        ldflags += [ "-mips64r6" ]
+      } else if (mips_arch_variant == "r2") {
+        cflags += [
+          "-mips64r2",
+          "-Wa,-mips64r2",
+        ]
+        ldflags += [ "-mips64r2" ]
+      }
+    }
+
+    defines += [ "_FILE_OFFSET_BITS=64" ]
+
+    if (!is_android) {
+      defines += [
+        "_LARGEFILE_SOURCE",
+        "_LARGEFILE64_SOURCE",
+      ]
+    }
+
+    # Omit unwind support in official builds to save space. We can use breakpad
+    # for these builds.
+    if (is_chrome_branded && is_official_build) {
+      cflags += [
+        "-fno-unwind-tables",
+        "-fno-asynchronous-unwind-tables",
+      ]
+      defines += [ "NO_UNWIND_TABLES" ]
+    } else {
+      cflags += [ "-funwind-tables" ]
+    }
+  }
+
+  if (enable_profiling && !is_debug) {
+    # The GYP build spams this define into every compilation unit, as we do
+    # here, but it only appears to be used in base and a couple other places.
+    # TODO(abarth): Should we move this define closer to where it's used?
+    defines += [ "ENABLE_PROFILING" ]
+
+    cflags += [
+      "-fno-omit-frame-pointer",
+      "-g",
+    ]
+
+    if (enable_full_stack_frames_for_profiling) {
+      cflags += [
+        "-fno-inline",
+        "-fno-optimize-sibling-calls",
+      ]
+    }
+  }
+
+  # Linux/Android common flags setup.
+  # ---------------------------------
+  if (is_linux || is_android) {
+    cflags += [
+      "-fPIC",
+      "-pipe",  # Use pipes for communicating between sub-processes. Faster.
+    ]
+
+    ldflags += [
+      "-fPIC",
+      "-Wl,-z,noexecstack",
+      "-Wl,-z,now",
+      "-Wl,-z,relro",
+    ]
+    if (!using_sanitizer) {
+      ldflags += [ "-Wl,-z,defs" ]
+    }
+  }
+
+  # Linux-specific compiler flags setup.
+  # ------------------------------------
+  if (is_linux) {
+    cflags += [ "-pthread" ]
+    ldflags += [ "-pthread" ]
+  }
+  if (use_gold) {
+    gold_path = rebase_path("//third_party/binutils/Linux_x64/Release/bin",
+                            root_build_dir)
+    ldflags += [
+      "-B$gold_path",
+
+      # Newer gccs and clangs support -fuse-ld, use the flag to force gold
+      # selection.
+      # gcc -- http://gcc.gnu.org/onlinedocs/gcc-4.8.0/gcc/Optimize-Options.html
+      "-fuse-ld=gold",
+
+      # Experimentation found that using four linking threads
+      # saved ~20% of link time.
+      # https://groups.google.com/a/chromium.org/group/chromium-dev/browse_thread/thread/281527606915bb36
+      # Only apply this to the target linker, since the host
+      # linker might not be gold, but isn't used much anyway.
+      # TODO(raymes): Disable threading because gold is frequently
+      # crashing on the bots: crbug.com/161942.
+      #"-Wl,--threads",
+      #"-Wl,--thread-count=4",
+    ]
+
+    if (!is_asan && !is_msan && !is_lsan && !is_tsan) {
+      # TODO(brettw) common.gypi has this only for target toolset.
+      ldflags += [ "-Wl,--icf=all" ]
+    }
+
+    # TODO(thestig): Make this flag work with GN.
+    #if (!is_official_build && !is_chromeos && !(is_asan || is_lsan || is_tsan || is_msan)) {
+    #  ldflags += [
+    #    "-Wl,--detect-odr-violations",
+    #  ]
+    #}
+  }
+
+  if (linux_use_bundled_binutils) {
+    binutils_path = rebase_path("//third_party/binutils/Linux_x64/Release/bin",
+                                root_build_dir)
+    cflags += [ "-B$binutils_path" ]
+  }
+
+  # Clang-specific compiler flags setup.
+  # ------------------------------------
+  if (is_clang) {
+    cflags += [ "-fcolor-diagnostics" ]
+  }
+
+  # C++11 compiler flags setup.
+  # ---------------------------
+  if (is_linux || is_android || is_nacl) {
+    # gnu++11 instead of c++11 is needed because some code uses typeof() (a
+    # GNU extension).
+    # TODO(thakis): Eventually switch this to c++11 instead,
+    # http://crbug.com/427584
+    cflags_cc += [ "-std=gnu++11" ]
+  } else if (!is_win) {
+    cc_std = [ "-std=c++11" ]
+    cflags_cc += cc_std
+    cflags_objcc += cc_std
+  }
+
+  # Android-specific flags setup.
+  # -----------------------------
+  if (is_android) {
+    cflags += [
+      "-ffunction-sections",
+      "-funwind-tables",
+      "-fno-short-enums",
+    ]
+    if (!is_clang) {
+      # Clang doesn't support these flags.
+      cflags += [ "-finline-limit=64" ]
+    }
+    if (is_asan) {
+      # Android build relies on -Wl,--gc-sections removing unreachable code.
+      # ASan instrumentation for globals inhibits this and results in a library
+      # with unresolvable relocations.
+      # TODO(eugenis): find a way to reenable this.
+      cflags += [ "-mllvm -asan-globals=0" ]
+    }
+
+    defines += [ "ANDROID" ]
+
+    # The NDK has these things, but doesn't define the constants
+    # to say that it does. Define them here instead.
+    defines += [ "HAVE_SYS_UIO_H" ]
+
+    # Use gold for Android for most CPU architectures.
+    if (current_cpu == "x86" || current_cpu == "x64" || current_cpu == "arm") {
+      ldflags += [ "-fuse-ld=gold" ]
+      if (is_clang) {
+        # Let clang find the ld.gold in the NDK.
+        ldflags += [ "--gcc-toolchain=" +
+                     rebase_path(android_toolchain_root, root_build_dir) ]
+      }
+    }
+
+    ldflags += [
+      "-Wl,--no-undefined",
+
+      # Don't allow visible symbols from libgcc or libc++ to be
+      # re-exported.
+      "-Wl,--exclude-libs=libgcc.a",
+      "-Wl,--exclude-libs=libc++_static.a",
+
+      # Don't allow visible symbols from libraries that contain
+      # assembly code with symbols that aren't hidden properly.
+      # http://crbug.com/448386
+      "-Wl,--exclude-libs=libvpx_assembly_arm.a",
+    ]
+    if (current_cpu == "arm") {
+      ldflags += [
+        # Enable identical code folding to reduce size.
+        "-Wl,--icf=safe",
+      ]
+    }
+
+    if (is_clang) {
+      if (current_cpu == "arm") {
+        cflags += [ "--target=arm-linux-androideabi" ]
+        ldflags += [ "--target=arm-linux-androideabi" ]
+      } else if (current_cpu == "x86") {
+        cflags += [ "--target=x86-linux-androideabi" ]
+        ldflags += [ "--target=x86-linux-androideabi" ]
+      }
+    }
+  }
+}
+
+config("compiler_arm_fpu") {
+  if (current_cpu == "arm" && !is_ios) {
+    cflags = [ "-mfpu=$arm_fpu" ]
+  }
+}
+
+# runtime_library -------------------------------------------------------------
+#
+# Sets the runtime library and associated options.
+#
+# How do you determine what should go in here vs. "compiler" above? Consider if
+# a target might choose to use a different runtime library (ignore for a moment
+# if this is possible or reasonable on your system). If such a target would want
+# to change or remove your option, put it in the runtime_library config. If a
+# target wants the option regardless, put it in the compiler config.
+
+config("runtime_library") {
+  cflags = []
+  defines = []
+  ldflags = []
+  lib_dirs = []
+  libs = []
+
+  if (is_component_build) {
+    # Component mode: dynamic CRT.
+    defines += [ "COMPONENT_BUILD" ]
+    if (is_win) {
+      # Since the library is shared, it requires exceptions or will give errors
+      # about things not matching, so keep exceptions on.
+      if (is_debug) {
+        cflags += [ "/MDd" ]
+      } else {
+        cflags += [ "/MD" ]
+      }
+    }
+  } else {
+    # Static CRT.
+    if (is_win) {
+      if (is_debug) {
+        cflags += [ "/MTd" ]
+      } else {
+        cflags += [ "/MT" ]
+      }
+    }
+  }
+
+  if (is_win) {
+    defines += [
+      "__STD_C",
+      "_CRT_RAND_S",
+      "_CRT_SECURE_NO_DEPRECATE",
+      "_HAS_EXCEPTIONS=0",
+      "_SCL_SECURE_NO_DEPRECATE",
+    ]
+  }
+
+  # Android standard library setup.
+  if (is_android) {
+    if (is_clang) {
+      # Work around incompatibilities between bionic and clang headers.
+      defines += [
+        "__compiler_offsetof=__builtin_offsetof",
+        "nan=__builtin_nan",
+      ]
+    }
+
+    defines += [ "__GNU_SOURCE=1" ]  # Necessary for clone().
+
+    # TODO(jdduke) Re-enable on mips after resolving linking
+    # issues with libc++ (crbug.com/456380).
+    if (current_cpu != "mipsel" && current_cpu != "mips64el") {
+      ldflags += [ "-Wl,--warn-shared-textrel" ]
+    }
+    ldflags += [ "-nostdlib" ]
+
+    # NOTE: The libc++ header include paths below are specified in cflags
+    # rather than include_dirs because they need to come after include_dirs.
+    # Think of them like system headers, but don't use '-isystem' because the
+    # arm-linux-androideabi-4.4.3 toolchain (circa Gingerbread) will exhibit
+    # strange errors. The include ordering here is important; change with
+    # caution.
+    cflags += [
+      "-isystem" +
+          rebase_path("$android_libcpp_root/libcxx/include", root_build_dir),
+      "-isystem" + rebase_path(
+              "$android_ndk_root/sources/cxx-stl/llvm-libc++abi/libcxxabi/include",
+              root_build_dir),
+      "-isystem" +
+          rebase_path("$android_ndk_root/sources/android/support/include",
+                      root_build_dir),
+    ]
+
+    lib_dirs += [ "$android_libcpp_root/libs/$android_app_abi" ]
+    libs += [ "$android_libcpp_library" ]
+
+    if (current_cpu == "mipsel") {
+      libs += [
+        # ld linker is used for mips Android, and ld does not accept library
+        # absolute path prefixed by "-l"; Since libgcc does not exist in mips
+        # sysroot the proper library will be linked.
+        # TODO(gordanac): Remove once gold linker is used for mips Android.
+        "gcc",
+      ]
+    } else {
+      libs += [
+        # Manually link the libgcc.a that the cross compiler uses. This is
+        # absolute because the linker will look inside the sysroot if it's not.
+        rebase_path(android_libgcc_file),
+      ]
+    }
+
+    libs += [
+      "c",
+      "dl",
+      "m",
+    ]
+
+    # Clang with libc++ does not require an explicit atomic library reference.
+    if (!is_clang) {
+      libs += [ "atomic" ]
+    }
+  }
+}
+
+# default_warning_flags collects all warning flags that are used by default.
+# This is in a variable instead of a config so that it can be used in
+# both chromium_code and no_chromium_code.  This way these flags are guaranteed
+# to appear on the compile command line after -Wall.
+
+default_warning_flags = []
+default_warning_flags_cc = []
+if (is_win) {
+  if (!is_clang || current_cpu != "x86") {
+    default_warning_flags += [ "/WX" ]  # Treat warnings as errors.
+  }
+
+  default_warning_flags += [
+    # Warnings permanently disabled:
+
+    # TODO(GYP) The GYP build doesn't have this globally enabled but disabled
+    # for a bunch of individual targets. Re-enable this globally when those
+    # targets are fixed.
+    "/wd4018",  # Comparing signed and unsigned values.
+
+    # C4127: conditional expression is constant
+    # This warning can in theory catch dead code and other problems, but
+    # triggers in far too many desirable cases where the conditional
+    # expression is either set by macros or corresponds some legitimate
+    # compile-time constant expression (due to constant template args,
+    # conditionals comparing the sizes of different types, etc.).  Some of
+    # these can be worked around, but it's not worth it.
+    "/wd4127",
+
+    # C4251: 'identifier' : class 'type' needs to have dll-interface to be
+    #        used by clients of class 'type2'
+    # This is necessary for the shared library build.
+    "/wd4251",
+
+    # C4351: new behavior: elements of array 'array' will be default
+    #        initialized
+    # This is a silly "warning" that basically just alerts you that the
+    # compiler is going to actually follow the language spec like it's
+    # supposed to, instead of not following it like old buggy versions did.
+    # There's absolutely no reason to turn this on.
+    "/wd4351",
+
+    # C4355: 'this': used in base member initializer list
+    # It's commonly useful to pass |this| to objects in a class' initializer
+    # list.  While this warning can catch real bugs, most of the time the
+    # constructors in question don't attempt to call methods on the passed-in
+    # pointer (until later), and annotating every legit usage of this is
+    # simply more hassle than the warning is worth.
+    "/wd4355",
+
+    # C4503: 'identifier': decorated name length exceeded, name was
+    #        truncated
+    # This only means that some long error messages might have truncated
+    # identifiers in the presence of lots of templates.  It has no effect on
+    # program correctness and there's no real reason to waste time trying to
+    # prevent it.
+    "/wd4503",
+
+    # Warning C4589 says: "Constructor of abstract class ignores
+    # initializer for virtual base class." Disable this warning because it
+    # is flaky in VS 2015 RTM. It triggers on compiler generated
+    # copy-constructors in some cases.
+    "/wd4589",
+
+    # C4611: interaction between 'function' and C++ object destruction is
+    #        non-portable
+    # This warning is unavoidable when using e.g. setjmp/longjmp.  MSDN
+    # suggests using exceptions instead of setjmp/longjmp for C++, but
+    # Chromium code compiles without exception support.  We therefore have to
+    # use setjmp/longjmp for e.g. JPEG decode error handling, which means we
+    # have to turn off this warning (and be careful about how object
+    # destruction happens in such cases).
+    "/wd4611",
+
+    # Warnings to evaluate and possibly fix/reenable later:
+
+    "/wd4100",  # Unreferenced formal function parameter.
+    "/wd4121",  # Alignment of a member was sensitive to packing.
+    "/wd4244",  # Conversion: possible loss of data.
+    "/wd4481",  # Nonstandard extension: override specifier.
+    "/wd4505",  # Unreferenced local function has been removed.
+    "/wd4510",  # Default constructor could not be generated.
+    "/wd4512",  # Assignment operator could not be generated.
+    "/wd4610",  # Class can never be instantiated, constructor required.
+    "/wd4996",  # Deprecated function warning.
+  ]
+
+  # VS xtree header file needs to be patched or 4702 (unreachable code
+  # warning) is reported if _HAS_EXCEPTIONS=0. Disable the warning if xtree is
+  # not patched.
+  if (!msvs_xtree_patched &&
+      exec_script("../../win_is_xtree_patched.py", [], "value") == 0) {
+    default_warning_flags += [ "/wd4702" ]  # Unreachable code.
+  }
+
+  # Building with Clang on Windows is a work in progress and very
+  # experimental. See crbug.com/82385.
+  # Keep this in sync with the similar block in build/common.gypi
+  if (is_clang) {
+    default_warning_flags += [
+      # TODO(hans): Make this list shorter eventually, http://crbug.com/504657
+      "-Qunused-arguments",  # http://crbug.com/504658
+      "-Wno-microsoft",  # http://crbug.com/505296
+      "-Wno-switch",  # http://crbug.com/505308
+      "-Wno-unknown-pragmas",  # http://crbug.com/505314
+      "-Wno-unused-function",  # http://crbug.com/505316
+      "-Wno-unused-value",  # http://crbug.com/505318
+      "-Wno-unused-local-typedef",  # http://crbug.com/411648
+    ]
+  }
+} else {
+  # Common GCC warning setup.
+  default_warning_flags += [
+    # Enables.
+    "-Wendif-labels",  # Weird old-style text after an #endif.
+    "-Werror",  # Warnings as errors.
+
+    # Disables.
+    "-Wno-missing-field-initializers",  # "struct foo f = {0};"
+    "-Wno-unused-parameter",  # Unused function parameters.
+  ]
+
+  if (is_mac) {
+    # TODO(abarth): Re-enable once https://github.com/domokit/mojo/issues/728
+    #               is fixed.
+    # default_warning_flags += [ "-Wnewline-eof" ]
+    if (!is_nacl) {
+      # When compiling Objective-C, warns if a method is used whose
+      # availability is newer than the deployment target. This is not
+      # required when compiling Chrome for iOS.
+      default_warning_flags += [ "-Wpartial-availability" ]
+    }
+  }
+
+  if (gcc_version >= 48) {
+    default_warning_flags_cc += [
+      # See comment for -Wno-c++11-narrowing.
+      "-Wno-narrowing",
+    ]
+  }
+
+  # Suppress warnings about ABI changes on ARM (Clang doesn't give this
+  # warning).
+  if (current_cpu == "arm" && !is_clang) {
+    default_warning_flags += [ "-Wno-psabi" ]
+  }
+
+  if (is_android) {
+    # Disable any additional warnings enabled by the Android build system but
+    # which chromium does not build cleanly with (when treating warning as
+    # errors).
+    default_warning_flags += [
+      "-Wno-extra",
+      "-Wno-ignored-qualifiers",
+      "-Wno-type-limits",
+    ]
+    default_warning_flags_cc += [
+      # Disabling c++0x-compat should be handled in WebKit, but
+      # this currently doesn't work because gcc_version is not set
+      # correctly when building with the Android build system.
+      # TODO(torne): Fix this in WebKit.
+      "-Wno-error=c++0x-compat",
+
+      # Other things unrelated to -Wextra:
+      "-Wno-non-virtual-dtor",
+      "-Wno-sign-promo",
+    ]
+  }
+
+  if (gcc_version >= 48) {
+    # Don't warn about the "typedef 'foo' locally defined but not used"
+    # for gcc 4.8.
+    # TODO: remove this flag once all builds work. See crbug.com/227506
+    default_warning_flags += [ "-Wno-unused-local-typedefs" ]
+  }
+}
+if (is_clang) {
+  default_warning_flags += [
+    # This warns on using ints as initializers for floats in
+    # initializer lists (e.g. |int a = f(); CGSize s = { a, a };|),
+    # which happens in several places in chrome code. Not sure if
+    # this is worth fixing.
+    "-Wno-c++11-narrowing",
+
+    # Don't die on dtoa code that uses a char as an array index.
+    # This is required solely for base/third_party/dmg_fp/dtoa.cc.
+    # TODO(brettw) move this to that project then!
+    "-Wno-char-subscripts",
+
+    # Warns on switches on enums that cover all enum values but
+    # also contain a default: branch. Chrome is full of that.
+    "-Wno-covered-switch-default",
+
+    # Clang considers the `register` keyword as deprecated, but e.g.
+    # code generated by flex (used in angle) contains that keyword.
+    # http://crbug.com/255186
+    "-Wno-deprecated-register",
+  ]
+
+  # NaCl's Clang compiler and Chrome's hermetic Clang compiler will almost
+  # always have different versions. Certain flags may not be recognized by
+  # one version or the other.
+  if (!is_nacl) {
+    # Flags NaCl does not recognize.
+    default_warning_flags += [
+      # TODO(hans): Get this cleaned up, http://crbug.com/428099
+      "-Wno-inconsistent-missing-override",
+
+      # TODO(thakis): Enable this, crbug.com/507717
+      "-Wno-shift-negative-value",
+    ]
+  }
+}
+
+# chromium_code ---------------------------------------------------------------
+#
+# Toggles between higher and lower warnings for code that is (or isn't)
+# part of Chromium.
+
+config("chromium_code") {
+  if (is_win) {
+    cflags = [ "/W4" ]  # Warning level 4.
+  } else {
+    cflags = [
+      "-Wall",
+      "-Wextra",
+    ]
+
+    # In Chromium code, we define __STDC_foo_MACROS in order to get the
+    # C99 macros on Mac and Linux.
+    defines = [
+      "__STDC_CONSTANT_MACROS",
+      "__STDC_FORMAT_MACROS",
+    ]
+
+    if (!using_sanitizer && (!is_linux || !is_clang || is_official_build)) {
+      # _FORTIFY_SOURCE isn't really supported by Clang now, see
+      # http://llvm.org/bugs/show_bug.cgi?id=16821.
+      # It seems to work fine with Ubuntu 12 headers though, so use it in
+      # official builds.
+      #
+      # Non-chromium code is not guaranteed to compile cleanly with
+      # _FORTIFY_SOURCE. Also, fortified build may fail when optimizations are
+      # disabled, so only do that for Release build.
+      defines += [ "_FORTIFY_SOURCE=2" ]
+    }
+  }
+  cflags += default_warning_flags
+  cflags_cc = default_warning_flags_cc
+}
+config("no_chromium_code") {
+  cflags = []
+  cflags_cc = []
+  defines = []
+
+  if (is_win) {
+    cflags += [
+      "/W3",  # Warning level 3.
+      "/wd4800",  # Disable warning when forcing value to bool.
+      "/wd4267",  # TODO(jschuh): size_t to int.
+      "/wd4996",  # Deprecated function warning.
+    ]
+    defines += [
+      "_CRT_NONSTDC_NO_WARNINGS",
+      "_CRT_NONSTDC_NO_DEPRECATE",
+    ]
+  }
+
+  if (is_linux) {
+    # Don't warn about ignoring the return value from e.g. close(). This is
+    # off by default in some gccs but on by default in others. BSD systems do
+    # not support this option, since they are usually using gcc 4.2.1, which
+    # does not have this flag yet.
+    cflags += [ "-Wno-unused-result" ]
+  }
+
+  if (is_clang) {
+    cflags += [
+      # TODO(mgiuca): Move this suppression into individual third-party
+      # libraries as required. http://crbug.com/505301.
+      "-Wno-overloaded-virtual",
+
+      # Lots of third-party libraries have unused variables. Instead of
+      # suppressing them individually, we just blanket suppress them here.
+      "-Wno-unused-variable",
+    ]
+  }
+
+  if (is_linux || is_android) {
+    cflags += [
+      # Don't warn about printf format problems. This is off by default in gcc
+      # but on in Ubuntu's gcc(!).
+      "-Wno-format",
+    ]
+    cflags_cc += [
+      # Don't warn about hash_map in third-party code.
+      "-Wno-deprecated",
+    ]
+  }
+  cflags += default_warning_flags
+  cflags_cc += default_warning_flags_cc
+}
+
+# rtti ------------------------------------------------------------------------
+#
+# Allows turning Run-Time Type Identification on or off.
+
+config("rtti") {
+  if (is_win) {
+    cflags_cc = [ "/GR" ]
+  }
+}
+config("no_rtti") {
+  if (is_win) {
+    cflags_cc = [ "/GR-" ]
+  } else {
+    rtti_flags = [ "-fno-rtti" ]
+    cflags_cc = rtti_flags
+    cflags_objcc = rtti_flags
+  }
+}
+
+# Warnings ---------------------------------------------------------------------
+
+# This will generate warnings when using Clang if code generates exit-time
+# destructors, which will slow down closing the program.
+# TODO(thakis): Make this a blacklist instead, http://crbug.com/101600
+config("wexit_time_destructors") {
+  # TODO: Enable on Windows too, http://crbug.com/404525
+  if (is_clang && !is_win) {
+    cflags = [ "-Wexit-time-destructors" ]
+  }
+}
+
+# On Windows compiling on x64, VC will issue a warning when converting
+# size_t to int because it will truncate the value. Our code should not have
+# these warnings and one should use a static_cast or a checked_cast for the
+# conversion depending on the case. However, a lot of code still needs to be
+# fixed. Apply this config to such targets to disable the warning.
+#
+# Note that this can be applied regardless of platform and architecture to
+# clean up the call sites. This will only apply the flag when necessary.
+#
+# TODO(jschuh): crbug.com/167187 fix this and delete this config.
+config("no_size_t_to_int_warning") {
+  if (is_win && current_cpu == "x64") {
+    cflags = [ "/wd4267" ]
+  }
+}
+
+# Optimization -----------------------------------------------------------------
+#
+# Note that BUILDCONFIG.gn sets up a variable "default_optimization_config"
+# which it will assign to the config it implicitly applies to every target. If
+# you want to override the optimization level for your target, remove this
+# config (which will expand differently for debug or release builds), and then
+# add back the one you want to override it with:
+#
+#   configs -= default_optimization_config
+#   configs += [ "//build/config/compiler/optimize_max" ]
+
+# Shared settings for both "optimize" and "optimize_max" configs.
+# IMPORTANT: On Windows "/O1" and "/O2" must go before the common flags.
+if (is_win) {
+  common_optimize_on_cflags = [
+    "/Ob2",  # Both explicit and auto inlining.
+    "/Oy-",  # Disable omitting frame pointers, must be after /O2.
+  ]
+  if (!is_asan) {
+    common_optimize_on_cflags += [
+      # Put data in separate COMDATs. This allows the linker
+      # to put bit-identical constants at the same address even if
+      # they're unrelated constants, which saves binary size.
+      # This optimization can't be used when ASan is enabled because
+      # it is not compatible with the ASan ODR checker.
+      "/Gw",
+    ]
+  }
+  common_optimize_on_ldflags = [ "/OPT:REF" ]
+} else {
+  common_optimize_on_cflags = [
+    # Don't emit the GCC version ident directives, they just end up in the
+    # .comment section taking up binary size.
+    "-fno-ident",
+
+    # Put data and code in their own sections, so that unused symbols
+    # can be removed at link time with --gc-sections.
+    "-fdata-sections",
+    "-ffunction-sections",
+  ]
+  common_optimize_on_ldflags = []
+
+  if (is_android) {
+    if (!using_sanitizer) {
+      common_optimize_on_cflags += [ "-fomit-frame-pointer" ]
+    }
+
+    # TODO(jdduke) Re-enable on mips after resolving linking
+    # issues with libc++ (crbug.com/456380).
+    if (current_cpu != "mipsel" && current_cpu != "mips64el") {
+      common_optimize_on_ldflags += [
+        # Warn in case of text relocations.
+        "-Wl,--warn-shared-textrel",
+      ]
+    }
+  }
+
+  if (is_mac || is_ios) {
+    if (symbol_level == 2) {
+      # Mac dead code stripping requires symbols.
+      common_optimize_on_ldflags += [ "-Wl,-dead_strip" ]
+    }
+  } else {
+    # Non-Mac Posix linker flags.
+    common_optimize_on_ldflags += [
+      # Specifically tell the linker to perform optimizations.
+      # See http://lwn.net/Articles/192624/ .
+      "-Wl,-O1",
+      "-Wl,--gc-sections",
+    ]
+
+    if (!using_sanitizer) {
+      # Functions interposed by the sanitizers can make ld think
+      # that some libraries aren't needed when they actually are,
+      # http://crbug.com/234010. As workaround, disable --as-needed.
+      common_optimize_on_ldflags += [ "-Wl,--as-needed" ]
+    }
+  }
+}
+
+# Default "optimization on" config. On Windows, this favors size over speed.
+config("optimize") {
+  if (is_win) {
+    # Favor size over speed, /O1 must be before the common flags. The GYP
+    # build also specifies /Os and /GF but these are implied by /O1.
+    cflags = [ "/O1" ] + common_optimize_on_cflags + [ "/Oi" ]
+  } else if (is_android || is_ios) {
+    cflags = [ "-Os" ] + common_optimize_on_cflags  # Favor size over speed.
+  } else {
+    cflags = [ "-O2" ] + common_optimize_on_cflags
+  }
+  ldflags = common_optimize_on_ldflags
+}
+
+# Turn off optimizations.
+config("no_optimize") {
+  if (is_win) {
+    cflags = [
+      "/Od",  # Disable optimization.
+      "/Ob0",  # Disable all inlining (on by default).
+      "/RTC1",  # Runtime checks for stack frame and uninitialized variables.
+    ]
+  } else if (is_android && !android_full_debug) {
+    # On Android we kind of optimize some things that don't affect debugging
+    # much even when optimization is disabled to get the binary size down.
+    cflags = [
+      "-Os",
+      "-fdata-sections",
+      "-ffunction-sections",
+    ]
+    if (!using_sanitizer) {
+      cflags += [ "-fomit-frame-pointer" ]
+    }
+    ldflags = common_optimize_on_ldflags
+  } else {
+    cflags = [ "-O0" ]
+  }
+}
+
+# Turns up the optimization level. On Windows, this implies whole program
+# optimization and link-time code generation which is very expensive and should
+# be used sparingly.
+config("optimize_max") {
+  ldflags = common_optimize_on_ldflags
+  if (is_win) {
+    # Favor speed over size, /O2 must be before the common flags. The GYP
+    # build also specifies /Ot, /Oi, and /GF, but these are implied by /O2.
+    cflags = [ "/O2" ] + common_optimize_on_cflags
+    if (is_official_build) {
+      # TODO(GYP): TODO(dpranke): Should these only be on in an official
+      # build, or on all the time? For now we'll require official build so
+      # that the compile is clean.
+      cflags += [
+        "/GL",  # Whole program optimization.
+
+        # Disable Warning 4702 ("Unreachable code") for the WPO/PGO builds.
+        # Probably anything that this would catch that wouldn't be caught in a
+        # normal build isn't going to actually be a bug, so the incremental
+        # value of C4702 for PGO builds is likely very small.
+        "/wd4702",
+      ]
+      ldflags += [ "/LTCG" ]
+    }
+  } else {
+    cflags = [ "-O2" ] + common_optimize_on_cflags
+  }
+}
+
+# Symbols ----------------------------------------------------------------------
+
+config("symbols") {
+  if (is_win) {
+    import("//build/toolchain/goma.gni")
+    if (use_goma) {
+      cflags = [ "/Z7" ]  # No PDB file
+    } else {
+      cflags = [ "/Zi" ]  # Produce PDB file, no edit and continue.
+    }
+    ldflags = [ "/DEBUG" ]
+  } else {
+    cflags = [ "-g2" ]
+    if (use_debug_fission) {
+      cflags += [ "-gsplit-dwarf" ]
+    }
+  }
+}
+
+config("minimal_symbols") {
+  if (is_win) {
+    # Linker symbols for backtraces only.
+    ldflags = [ "/DEBUG" ]
+  } else {
+    cflags = [ "-g1" ]
+    if (use_debug_fission) {
+      cflags += [ "-gsplit-dwarf" ]
+    }
+  }
+}
+
+config("no_symbols") {
+  if (!is_win) {
+    cflags = [ "-g0" ]
+  }
+}