Introduce background.scripts feature for extension manifests.

This optimizes for the common use case where background pages
just include a reference to one or more script files and no
additional HTML.

BUG=107791


Review URL: http://codereview.chromium.org/9150008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@117110 0039d316-1c4b-4281-b951-d872f2087c98
void TestingAutomationProvider::GetTabCount(int handle, int* tab_count) {
  *tab_count = -1;  // -1 is the error code

  if (browser_tracker_->ContainsHandle(handle)) {
    Browser* browser = browser_tracker_->GetResource(handle);
    *tab_count = browser->tab_count();
  }
}

void TestingAutomationProvider::GetTabCount(int handle, int* tab_count) {
  *tab_count = -1;  // -1 is the error code

  if (browser_tracker_->ContainsHandle(handle)) {
    Browser* browser = browser_tracker_->GetResource(handle);
    *tab_count = browser->tab_count();
  }
}
