Change Android toolchain to GCC 4.9.

build/config/compiler/BUILD.gn

Index: build/config/compiler/BUILD.gn
diff --git a/build/config/compiler/BUILD.gn b/build/config/compiler/BUILD.gn
index 0eddb2ce95b07aa5719e095abefebdc4e3598123..fc4478a3146efde82f9d979526ee1fdf40807e30 100644
--- a/build/config/compiler/BUILD.gn
+++ b/build/config/compiler/BUILD.gn
@@ -146,6 +146,21 @@ config("compiler") {
             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",
+          ]
+        }
       }
     }
 
@@ -239,15 +254,6 @@ config("compiler") {
       # 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) {