win: Add /d2Zi+ to compile flags

This makes debugging and stacks in Release builds much more accurate
(locals, arguments, information about inlining, etc.). The drawback is
somewhat larger .pdb files. Here's the sizes for the top 10 pdbs:

With /d2Zi+
-----------
07/17/2014  09:52 PM       280,408,064 content_unittests.exe.pdb
07/17/2014  09:47 PM       477,401,088 blink_web.dll.pdb
07/17/2014  09:50 PM       506,949,632 content.dll.pdb
07/17/2014  10:01 PM       955,576,320 sync_performance_tests.exe.pdb
07/17/2014  09:59 PM       955,912,192 performance_browser_tests.exe.pdb
07/17/2014  10:04 PM       965,382,144 sync_integration_tests.exe.pdb
07/17/2014  09:59 PM       987,688,960 chrome.dll.pdb
07/17/2014  10:03 PM     1,228,763,136 interactive_ui_tests.exe.pdb
07/17/2014  10:05 PM     1,398,632,448 browser_tests.exe.pdb
07/17/2014  10:07 PM     1,569,222,656 unit_tests.exe.pdb

Without
-------

07/17/2014  10:44 PM       238,104,576 content_unittests.exe.pdb
07/17/2014  10:39 PM       399,175,680 blink_web.dll.pdb
07/17/2014  10:44 PM       439,767,040 content.dll.pdb
07/17/2014  10:57 PM       837,832,704 sync_performance_tests.exe.pdb
07/17/2014  10:51 PM       838,119,424 performance_browser_tests.exe.pdb
07/17/2014  10:57 PM       846,286,848 sync_integration_tests.exe.pdb
07/17/2014  10:51 PM       864,194,560 chrome.dll.pdb
07/17/2014  10:58 PM     1,071,509,504 interactive_ui_tests.exe.pdb
07/17/2014  10:58 PM     1,219,203,072 browser_tests.exe.pdb
07/17/2014  10:58 PM     1,351,118,848 unit_tests.exe.pdb

So there is appreciable growth (~15%). The limit is currently 4G, so it
seems worth turning on for now, and if we must disable it later, we can.

R=wfh@chromium.org
BUG=350018,388264

Review URL: https://codereview.chromium.org/399843007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@284043 0039d316-1c4b-4281-b951-d872f2087c98

build/common.gypi

@@ -3235,7 +3235,10 @@
                 'AdditionalOptions': ['/Oy-'],
               }],
             ],
-            'AdditionalOptions': [ '<@(win_release_extra_cflags)', ],
+            'AdditionalOptions': [
+                '/d2Zi+',  # Improve debugging of Release builds.
+                '<@(win_release_extra_cflags)',
+            ],
           },
           'VCLinkerTool': {
             # LinkIncremental is a tri-state boolean, where 0 means default