[android] Bump up toolchain version.

BUG=chromium:502176
LOG=n

Review URL: https://codereview.chromium.org/1193843002

Cr-Commit-Position: refs/heads/master@{#29138}

Makefile.android

@@ -50,39 +50,33 @@ ifeq ($(ARCH), android_arm)
   DEFINES += arm_neon=0 arm_version=7
   TOOLCHAIN_ARCH = arm-linux-androideabi
   TOOLCHAIN_PREFIX = $(TOOLCHAIN_ARCH)
-  TOOLCHAIN_VER = 4.8
 else ifeq ($(ARCH), android_arm64)
   DEFINES  = target_arch=arm64 v8_target_arch=arm64 android_target_arch=arm64 android_target_platform=21
   TOOLCHAIN_ARCH = aarch64-linux-android
   TOOLCHAIN_PREFIX = $(TOOLCHAIN_ARCH)
-  TOOLCHAIN_VER = 4.9
 else ifeq ($(ARCH), android_mipsel)
   DEFINES  = target_arch=mipsel v8_target_arch=mipsel android_target_platform=21
   DEFINES += android_target_arch=mips mips_arch_variant=mips32r2
   TOOLCHAIN_ARCH = mipsel-linux-android
   TOOLCHAIN_PREFIX = $(TOOLCHAIN_ARCH)
-  TOOLCHAIN_VER = 4.8
 else ifeq ($(ARCH), android_ia32)
   DEFINES = target_arch=ia32 v8_target_arch=ia32 android_target_arch=x86 android_target_platform=21
   TOOLCHAIN_ARCH = x86
   TOOLCHAIN_PREFIX = i686-linux-android
-  TOOLCHAIN_VER = 4.8
 else ifeq ($(ARCH), android_x64)
   DEFINES = target_arch=x64 v8_target_arch=x64 android_target_arch=x86_64 android_target_platform=21
   TOOLCHAIN_ARCH = x86_64
   TOOLCHAIN_PREFIX = x86_64-linux-android
-  TOOLCHAIN_VER = 4.9
 else ifeq ($(ARCH), android_x87)
   DEFINES = target_arch=x87 v8_target_arch=x87 android_target_arch=x86 android_target_platform=21
   TOOLCHAIN_ARCH = x86
   TOOLCHAIN_PREFIX = i686-linux-android
-  TOOLCHAIN_VER = 4.8
 else
   $(error Target architecture "${ARCH}" is not supported)
 endif
 
 TOOLCHAIN_PATH = \
-    ${ANDROID_NDK_ROOT}/toolchains/${TOOLCHAIN_ARCH}-${TOOLCHAIN_VER}/prebuilt
+    ${ANDROID_NDK_ROOT}/toolchains/${TOOLCHAIN_ARCH}-4.9/prebuilt
 ANDROID_TOOLCHAIN ?= ${TOOLCHAIN_PATH}/${TOOLCHAIN_DIR}
 
 ifeq ($(wildcard $(ANDROID_TOOLCHAIN)),)