Update to Chromium revision 788460a4 (#345352)

- Mac: 10.10 SDK is now required for building (see http://crbug.com/463170#c63).
  Older SDKs can be used for a short time by setting mac_sdk_min via GYP_DEFINES.

patch/patches/public_browser_1257.patch

@@ -25,7 +25,7 @@ index 887f242..a7cc318 100644
  WebContents::CreateParams::~CreateParams() {
  }
 diff --git web_contents.h web_contents.h
-index 4ed6a40..2bbba64 100644
+index 803b816..1457ef3 100644
 --- web_contents.h
 +++ web_contents.h
 @@ -52,9 +52,11 @@ class PageState;