Reland "Bump macOS SDK to 10.12."

This is a reland of f5345de1.
The problem with blink trybots was fixed: 
https://bugs.chromium.org/p/chromium/issues/detail?id=669240#c45

Original change's description:
> Bump macOS SDK to 10.12.
> 
> Bug: 669240
> Change-Id: I97cf582b97fac7aec2aa92bbdda02f5c17482c1d
> Reviewed-on: https://chromium-review.googlesource.com/570459
> Reviewed-by: Erik Chen <erikchen@chromium.org>
> Reviewed-by: Nico Weber <thakis@chromium.org>
> Commit-Queue: Erik Chen <erikchen@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#491060}

Bug: 669240
Change-Id: I73b54eedbd0eab105adecfb6e817de8aa2b968ef
TBR: thakis@chromium.org
Reviewed-on: https://chromium-review.googlesource.com/598670Reviewed-by: Erik Chen <erikchen@chromium.org>
Commit-Queue: Erik Chen <erikchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#491499}

build/config/mac/mac_sdk_overrides.gni

@@ -9,7 +9,7 @@ _sdk_min_from_env = getenv("FORCE_MAC_SDK_MIN")
 declare_args() {
   # Minimum supported version of the Mac SDK.
   if (_sdk_min_from_env == "") {
-    mac_sdk_min = "10.10"
+    mac_sdk_min = "10.12"
   } else {
     mac_sdk_min = _sdk_min_from_env
   }
@@ -18,5 +18,5 @@ declare_args() {
 # Always assert that mac_sdk_min is used on non-macOS platforms to prevent
 # unused args warnings.
 if (!is_mac) {
-  assert(mac_sdk_min == "10.10" || true)
+  assert(mac_sdk_min == "10.12" || true)
 }

chrome/browser/ui/cocoa/ssl_client_certificate_selector_cocoa.mm

@@ -115,13 +115,12 @@ namespace {
 // an NSTableView. Future events may make cause the table view to query its
 // dataSource, which will have been deallocated.
 //
-// NSTableView.dataSource becomes a zeroing weak reference starting in 10.11,
-// so this workaround can be removed once we're on the 10.11 SDK.
+// Linking against the 10.12 SDK does not "fix" this issue, since
+// NSTableView.dataSource is a "weak" reference, which in non-ARC land still
+// translates to "raw pointer".
 //
-// See https://crbug.com/653093 and rdar://29409207 for more information.
-
-#if !defined(MAC_OS_X_VERSION_10_11) || \
-    MAC_OS_X_VERSION_MAX_ALLOWED < MAC_OS_X_VERSION_10_11
+// See https://crbug.com/653093, https://crbug.com/750242 and rdar://29409207
+// for more information.
 
 void ClearTableViewDataSources(NSView* view) {
   if (auto table_view = base::mac::ObjCCast<NSTableView>(view)) {
@@ -151,12 +150,6 @@ void ClearTableViewDataSourcesIfNeeded(NSWindow* leaked_window) {
                             base::Unretained(leaked_window)));
 }
 
-#else
-
-void ClearTableViewDataSourcesIfNeeded(NSWindow*) {}
-
-#endif  // MAC_OS_X_VERSION_10_11
-
 }  // namespace
 
 @implementation SSLClientCertificateSelectorCocoa