Re-enable various MSVC warnings.

build/common.gypi

Index: build/common.gypi
diff --git a/build/common.gypi b/build/common.gypi
index 7be6ee083d1e0a0924755dce83c40fee6d392c14..6d619e53bfdf93117ce5773b1e0d8b040da0b103 100644
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -5277,11 +5277,60 @@
         ],
         'msvs_cygwin_shell': 0,
         'msvs_disabled_warnings': [
-          4351, 4355, 4396, 4503, 4819,
+          # C4127: conditional expression is constant
+          # This warning can in theory catch dead code and other problems, but
+          # triggers in far too many desirable cases where the conditional
+          # expression is either set by macros or corresponds some legitimate
+          # compile-time constant expression (due to constant template args,
+          # conditionals comparing the sizes of different types, etc.).  Some of
+          # these can be worked around, but it's not worth it.
+          4127,
+
+          # C4351: new behavior: elements of array 'array' will be default
+          #        initialized
+          # This is a silly "warning" that basically just alerts you that the
+          # compiler is going to actually follow the language spec like it's
+          # supposed to, instead of not following it like old buggy versions
+          # did.  There's absolutely no reason to turn this on.
+          4351,
+
+          # C4355: 'this': used in base member initializer list
+          # It's commonly useful to pass |this| to objects in a class'
+          # initializer list.  While this warning can catch real bugs, most of
+          # the time the constructors in question don't attempt to call methods
+          # on the passed-in pointer (until later), and annotating every legit
+          # usage of this is simply more hassle than the warning is worth.
+          4355,
+
+          # C4503: 'identifier': decorated name length exceeded, name was
+          #        truncated
+          # This only means that some long error messages might have truncated
+          # identifiers in the presence of lots of templates.  It has no effect
+          # on program correctness and there's no real reason to waste time
+          # trying to prevent it.
+          4503,
+          
+          # C4611: interaction between 'function' and C++ object destruction is
+          #        non-portable
+          # This warning is unavoidable when using e.g. setjmp/longjmp.  MSDN
+          # suggests using exceptions instead of setjmp/longjmp for C++, but
+          # Chromium code compiles without exception support.  We therefore have
+          # to use setjmp/longjmp for e.g. JPEG decode error handling, which
+          # means we have to turn off this warning (and be careful about how
+          # object destruction happens in such cases).
+          4611,
+
           # TODO(maruel): These warnings are level 4. They will be slowly
           # removed as code is fixed.
-          4100, 4121, 4125, 4127, 4130, 4131, 4189, 4201, 4238, 4244, 4245,
-          4310, 4428, 4481, 4505, 4510, 4512, 4530, 4610, 4611, 4701, 4706,
+          4100, # Unreferenced formal parameter
+          4121, # Alignment of a member was sensitive to packing
+          4189, # Local variable is initialized but not referenced
+          4244, # Conversion from 'type1' to 'type2', possible loss of data
+          4481, # Nonstandard extension used: override specifier 'keyword'
+          4505, # Unreferenced local function has been removed
+          4510, # Default constructor could not be generated
+          4512, # Assignment operator could not be generated
+          4610, # Object can never be instantiated
         ],
         'msvs_settings': {
           'VCCLCompilerTool': {