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 142 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.
+            "-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 76 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 632 matching lines @@
       cflags += [ "-gsplit-dwarf" ]
     }
   }
 }
 
 config("no_symbols") {
   if (!is_win) {
     cflags = [ "-g0" ]
   }
 }