Change Android toolchain to GCC 4.9.

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")
 if (cpu_arch == "arm") {
   import("//build/config/arm.gni")
 }
 if (is_posix) {
   import("//build/config/gcc/gcc_version.gni")
@@ skipping 128 matching lines @@
         ]
         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.
+            # TODO(fdegans) Reevaluate when we upgrade GCC.

[pasko, 2014/07/28 13:14:30]

Repeating yourself is boring. Let's have only one instance of these comments in
the most relevant place. It's relatively easy to find the reasons in the
codebase with git grep, and comments will be there.

[Fabrice (no longer in Chrome), 2014/07/28 13:40:43]

I removed the TODO (as per previous comment).
AFAIK, the long-term plan is to switch to gn and remove gyp. And some people do
not check the gn equivalent when doing toolchain changes(they should, but that's
another debate). So the comments will need to appear in both places for the time
being.

[brettw, 2014/07/28 17:56:14]

Yes, please duplicate the comment.

[pasko, 2014/07/28 18:22:27]

I was wrong: I thought this section is only about clang, and GCC is elsewhere.
You are right, we should have the same comments in GN.

+            "-fno-caller-saves",
+          ]
+        }
       }
     }
 
     defines += [ "_FILE_OFFSET_BITS=64" ]
 
     # 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",
@@ skipping 73 matching lines @@
   if (is_android) {
     cflags += [
       "-ffunction-sections",
       "-funwind-tables",
       "-fno-short-enums",
     ]
     if (!is_clang) {
       # Clang doesn't support these flags.
       cflags += [
         "-finline-limit=64",
-        # The following 6 options are disabled to save on
-        # binary size in gcc 4.8.
-        # TODO(fdegans) Reevaluate when we upgrade GCC.
-        "-fno-partial-inlining",
-        "-fno-early-inlining",
-        "-fno-tree-copy-prop",
-        "-fno-tree-loop-optimize",
-        "-fno-move-loop-invariants",
-        "-fno-caller-saves",
       ]
     }
     if (is_android_webview_build) {
       # Android predefines this as 1; undefine it here so Chromium can redefine
       # it later to be 2 for chromium code and unset for third party code. This
       # works because cflags are added before defines.
       # TODO(brettw) the above comment seems incorrect. We specify defines
       # before cflags on our compiler command lines.
       cflags += [ "-U_FORTIFY_SOURCE" ]
     }
@@ skipping 585 matching lines @@
   } else {
     cflags = [ "-g1" ]
   }
 }
 
 config("no_symbols") {
   if (!is_win) {
     cflags = [ "-g0" ]
   }
 }