* Output of `node_modules/.bin/electron --version`: 3.0.9 (and up)
* Operating System (Platform and Version): Windows 10
* Output of `node_modules/.bin/electron --version` on last known working Electron version (if applicable): 2.0.x

**Expected Behavior**
Pressing `Ctrl + Shift + V` should result in one paste event only.

**Actual behavior**
Pressing `Ctrl + Shift + V` results in two paste events only.

**To Reproduce**
@brenca was nice enough to make a Fiddle (https://gist.github.com/brenca/e0ca153755979bed51a991e9d8c185bb). 

**Additional Notes**
A few notes that are interesting:
 * This bug is Windows-only.
 * Not registering a `paste` handler: No issue
 * Not calling `event.preventDefault()` or `event.returnValue = false`: No issue
 * Just clicking on a `MenuItem` that calls `webContents.pasteAndMatchStyle()`: No issue
 * Not registering a `MenuItem` with an accelerator: No issue
 * Chromium 66 does not have this issue


atom/browser/ui/accelerator_util.cc
#include "atom/browser/ui/accelerator_util.h"
#include <stdio.h>
#include <string>
#include <vector>
#include "atom/common/keyboard_util.h"
#include "base/stl_util.h"
#include "base/strings/string_number_conversions.h"
#include "base/strings/string_split.h"
#include "base/strings/string_util.h"
namespace accelerator_util {
bool StringToAccelerator(const std::string& shortcut,
                         ui::Accelerator* accelerator) {
  if (!base::IsStringASCII(shortcut)) {
    LOG(ERROR) << "The accelerator string can only contain ASCII characters";
    return false;
  }
  std::vector<std::string> tokens = base::SplitString(
      shortcut, "+", base::TRIM_WHITESPACE, base::SPLIT_WANT_NONEMPTY);
  
  int modifiers = ui::EF_NONE;
  ui::KeyboardCode key = ui::VKEY_UNKNOWN;
  for (const auto& token : tokens) {
    bool shifted = false;
    ui::KeyboardCode code = atom::KeyboardCodeFromStr(token, &shifted);
    if (shifted)
      modifiers |= ui::EF_SHIFT_DOWN;